JP4155185B2 - Content distribution method, content distribution server, and content receiving apparatus - Google Patents

Description

  The present invention dynamically switches and transmits tracks in a content distribution system including a content distribution server that transmits content data composed of a plurality of tracks and a content reception device that receives and reproduces the content data via a network. The present invention relates to a content distribution method capable of smoothly reproducing a switched portion, a content distribution server using the content distribution method, and a content receiving device.

  First, an asynchronous model of a streaming system used for real-time distribution of video / audio will be described.

  There is no synchronization clock between two end-to-end communication devices in a data link based on the exchange of transmission frames of small data size represented by Ethernet (registered trademark) (IEEE802.3). In most cases, IP (Internet Protocol, RFC791, RFC2460) is used to enable packet exchange between multiple networks with the data link as the lower layer, and IP packets are used as sessions (communications) with IP as the lower layer. There is no synchronization clock in network protocols such as TCP (Transmission Control Protocol, RFC793) and UDP (User Datagram Protocol, RFC768) for performing path management.

  Therefore, it is not guaranteed when and when a transmission frame transmitted from a certain communication device arrives at the target communication device. Also, the time delay that occurs from transmission to reception of the transmission frame is not constant, and time fluctuation (jitter) occurs. Also, transmission frames may be lost on the transmission path, and even if a plurality of transmission frames are transmitted along a certain time axis, the arrival order is not guaranteed.

  By the way, a streaming system is a generic name of systems that receive and reproduce content via a network and that can reproduce while receiving without accumulating all of the content on the receiving side. Since video, audio, etc. are contents with real-time properties, playback synchronization control such as playback at a predetermined number of frames per second (eg 29.97 frames / second) is essential, and the presence of a synchronization clock is suitable. It can be said that there is. For example, in TV broadcasting, there is a synchronization clock called a frame synchronization signal in the NTSC_TV signal, and the reception side can reproduce it with very high accuracy using the synchronization clock on the transmission side.

  However, in a streaming system via an IP network based on IP, there is no synchronization clock as described above, and the transmission side and the reception side cannot be synchronized. Inevitably, the playback mechanism must be realized by an asynchronous model. The asynchronous model is a configuration and programming technique that operates based on the system clock of each device itself.

  FIG. 8 shows a functional block diagram of the content distribution server 102a and the content receiving device 103a in the content distribution system 101a (asynchronous model). The content distribution server 102a and the content receiving device 103a are connected to each other by the IP network 104.

  The content distribution server 102a includes a content acquisition unit 1021, a transmission unit 1022, a system clock oscillation unit 1023, and a content storage unit 1024.

  The content acquisition unit 1021 has a function of recording content data of content to be reproduced in the content storage unit 1024 and acquiring a content fragment using an arbitrary file pointer (reading position on the content). At this time, the file pointer is any one of the content file name, the track number, and the frame number, or some combination thereof. A “content segment” refers to actual data of content having an arbitrary data length.

  The content acquisition unit 1021 reads the content segment according to the system clock signal. The content acquisition unit 1021 has initial values such as a content file name, a track number, and a frame number inside, and may automatically start reading from the time of startup, or the content file name, track number, and content from an external input Reading may be started after the reproduction start time is obtained. Further, an external input for receiving command input is provided, and when command input = reproduction start constant (for example, “PLAY”), reproduction may be performed, or command input = reproduction stop constant (for example, “STOP”). If so, it may be stopped. Alternatively, the automatic read start operation and the external read start operation may be automatically determined.

  The system clock oscillator 1023 is a real-time clock (high-precision clock) realized by a crystal oscillator or the like, and has a function of supplying a system clock signal to the content acquisition unit.

  The transmission unit 1022 has a function of securing a virtual communication path called a session, packetizing the content fragment with an appropriate header, and transmitting the packet to the content reception device 103a via the IP network 104. Have. For example, the header includes a network time stamp (described later).

  When transmitting a packet, the transmission unit 1022 uses a transmission address to deliver the packet to the content reception device 103a. The transmission address is composed of a combination of a transmission address and a transmission port number. The transmission address may be previously stored as a constant in the transmission unit 1022 or may be input from another block. Note that a session (communication path) for transmitting a packet is dynamically established when a transmission address is determined. Further, the content segment and the packet do not necessarily match.

  In addition, the content receiving apparatus 103a includes a receiving unit 1031, a buffer unit 1032, a system clock oscillation unit 1033, a content reading unit 1034, and a reproduction unit 1035.

  The receiving unit 1031 has a function of receiving a packet from the IP network 104, interpreting the header, taking out a content fragment, and supplying it to the buffer unit 1032. The receiving unit 1031 uses a reception address in order to receive only a packet necessary for itself among the packets from the content distribution server 102a. The reception address is composed of a combination of a reception address and a reception port number. The reception address may be previously stored as a constant in the reception unit 1031 or may be input from another block.

  The buffer unit 1032 has a function of temporarily accumulating and storing content pieces together with a network time stamp (described later) obtained from the header.

  The content reading unit 1034 monitors the buffer unit 1032 and starts reading the content unit according to the system clock signal from the system clock oscillation unit 1033 from the time when it is determined that the content unit sufficient for reproduction has been accumulated. It has a function of restoring and outputting a set of segments as content.

  The playback unit 1035 has a function of performing decoding according to the input content segment and outputting an audio signal and a video signal to a predetermined output device such as a speaker. For example, when the content segment is high-efficiency encoded digital audio data similar to MPEG, the playback unit 1035 includes a high-efficiency code decoder (decoder), a D / A converter, an analog amplifier, and the like. Is done.

  The first feature of the content distribution system a (asynchronous model) shown in FIG. 8 is that the content distribution server 102a and the content receiving device 103a individually have system clock oscillation units 1023 and 1033, respectively. Although the accuracy of both system clock frequencies needs to be considerably high, the IP network 104 serving as a transmission path does not include a synchronous clock transmission mechanism.

  The second feature is that the content receiving device 103a includes the buffer unit 1032 and the content reading unit 1034 is configured so that the buffer unit 1032 is not emptied. Even in the case of reproducing content having a delay, normal reproduction is continued while absorbing time delay and time fluctuation (jitter) of packets caused by the IP network 104.

  The above is the outline of the asynchronous model of the streaming system used for real-time distribution of video / audio.

  Next, playback time management in the streaming system will be described.

  First, a method for assigning content playback time will be described.

  In the above asynchronous model, in order for content to be played back as a continuous medium at the correct playback time, it is necessary to transmit the content playback time in association with the content segment. For example, in FIG. 8, in order for the content reading unit 1034 to select a content segment corresponding to the 0 second 0 frame video and output it to the playback unit 1035, the content segment is the 0 second 0 frame. Content playback time indicating data is required. Otherwise, if a time delay or the like occurs on the network, the playback time will be shifted as it is.

  In streaming systems, RTP (Real-time Transfer Protocol, RFC1889) is often used to give content playback time to content pieces (Audio-Video Transport Working Group, "RTP: A Transport Protocol for Real- Time Applications ", RFC 1889, Internet Engineering Taskforce, Jan 1996). In RTP, the content fragment is the payload (cargo), and it is mainly composed of an RTP header with a minimum of 96 bits given prior to the payload, 32 bits of which are network time stamps (modified content playback time) ).

  The RTP time stamp is mapped in real time by the RTP time stamp frequency determined in advance by the content type. The RTP timestamp frequency is also called a network timestamp frequency. In general, in the case of content digitized by a high-efficiency encoding method defined by MPEG (Motion Picture Experts Group), 90000 (90 KHz) is often used as the RTP timestamp frequency. This means that when reading 1 second of content, the RTP timestamp is incremented by +90000. That is, the following formula is established for the network time stamp, the network time stamp frequency, and the content playback time similar to the RTP time stamp.

<Equation 1>
Content playback time = network time stamp / network time stamp frequency For example, in the case of MPEG-2 video at 29.97fps, if the RTP time stamp of the first frame is "0", the second frame is "3003", The 30th frame is “90090”.

  In the case of MPEG-4 Audio AAC, one frame is fixed at 1024 samples, and the RTP timestamp frequency uses the PCM sampling frequency of the sound source. For example, if the PCM sampling frequency is 44100Hz (44.1KHz PCM = CD Audio), the RTP timestamp frequency is 44100, the RTP timestamp of the first frame is “0”, the second frame is “1024”, approximately 1 second The 43rd frame corresponding to is “44032”.

  In this example, RTP has been described as an example, but there are other packet formats that can be used to calculate the content playback time on the receiving side from the network time stamp provided for the playback time and the corresponding network time stamp frequency. Yes, very common. For example, the MPEG-2 Transport Stream standardized by MPEG standardizes a time stamp called a “Presentation Time Stamp” having exactly the same function. The above is the outline of the content reproduction time giving method.

  Next, a data structure of a file (hereinafter referred to as a content file) in which content managed by the content distribution server 102a and transmitted to the content receiving device is recorded will be described.

  FIG. 9 shows an example of the data structure of content data managed by the content acquisition unit 1021. As shown in FIG. 9, the content data is composed of a content file name, the total number of tracks T, and the track data of each track. The track data of each track further includes a track number, a track time stamp frequency, the total number of frames, And a plurality of data frames composed of frame numbers, time information, and content pieces.

  The content file name is a name that uniquely identifies a file that stores content data on the content storage unit. The total number of tracks records the number of tracks contained in one content data. A track refers to each of a plurality of contents stored in one file, and an arbitrary track (content) can be selected by a track number, and is taken out from an arbitrary position by time information as a pointer. be able to. The track time stamp frequency recorded in each track indicates an increment per unit time of time information.

  In addition, the total number of frames, which is the total number of content segments, is recorded in each track, but the total number of frames may not be the same for each track. In addition, frame numbers are assigned to each content segment in time series, and time information based on the track timestamp frequency is assigned.

  The data structure of content data in which a plurality of contents are multiplexed as described above is very common as a file format for storing audio / moving images. Depending on the file format, the track time stamp frequency may not be included in the data as a system constant, or frames with the same time information may be indexed to save the time information storage area. However, the frame number and the time information are held in a mutually convertible state in common.

  Examples of such file formats include Microsoft AVI, Apple Computer QuickTime Format, and ISO / IEC 14496-1 MP4 File. In addition, in Apple Computer QuickTime Format and ISO / IEC 14496-1 MP4 File, by using Reference Atom (Data Reference Atom), all or part of the contents of multiple tracks can be made independent as external content data. However, since the frame number and time information are recorded in the main content data in a mutually convertible state, it may be regarded as having the same data structure as the content data. The above is the outline of the data structure of the content data in the content distribution server 102a.

  Next, the reproduction time management process (transmission side) of the content acquisition unit 1021 when reading content data will be described with reference to the flowchart of FIG.

  First, when a content reproduction request is received from the content receiving apparatus 103a, the content acquisition unit 1021 of the content distribution server 102a initializes the following six variables (step S101).

1: Content file name CF = Default content file name (eg "hoge.mp4")
2: Track number TN = default track number (eg "1")
3: Start frame number FN = default frame number (for example, “1”)
4: Playback start time STS = current time NTS obtained from the system clock oscillator 1023
5: Content playback time CTS = “0”
6: Playback state flag F = true value “N”
Next, the content acquisition unit 1021 refers to a predetermined automatic mode constant indicating whether or not to automatically start reproduction, and determines whether to perform automatic reproduction (step S102). When the automatic mode constant is the true value “Y”, the process proceeds to step S110, and when the automatic mode constant is the true value “N”, the process proceeds to step S103.

  In the process of step S102, if the constant is a true / false value “N”, the content acquisition unit 1021 determines that the external input (command input CMD, content file name CF1, track number TN1, content reproduction start time CTS1 4) It is determined whether or not there is a set of two variables (step S103). If there is an external input, the truth value is “Y” and the process proceeds to step S104. If there is no external input, the truth value is “N”. The process proceeds to step S106.

  In the process of step S103, when the automatic mode constant is a true / false value “Y”, the content acquisition unit 1021 determines whether command input CMD = reproduction stop constant among external inputs (step S104). When the command input CMD = reproduction stop constant, the truth value “Y” is obtained, and the entire operation is stopped. Otherwise, the truth value “N” is obtained, and the process proceeds to step S105.

  In the process of step S104, when the truth value is “N”, the content acquisition unit 1021 uses three variables of external input (content file name CF1, track number TN1, content playback start time CTS1), First, five variables are initialized (step S105).

1: Content file name CF = Content file name CF1
2: Track number TN = Track number TN1
3: Playback start time STS = current time NTS obtained from the system clock oscillator 1023
4: Content playback time CTS = Content playback start time CTS1
5: Playback state flag F = true value “Y”
Subsequently, the content acquisition unit 1021 initializes the start frame number FN using the content reproduction time CTS, and calculates transmission start time information StartTS as a previous step. The calculation formula of the transmission start time information StartTS is shown below.

<Equation 2>
StartTS = CTS × TRS
Here, the track time stamp frequency TRS is the track time stamp frequency of the track indicated by the track number TN in the content file name CF.

  Next, the content acquisition unit 1021 searches the frame number of the track indicated by the track number TN in the content file name CF in order from 1 to obtain the frame number NFN of the point where time information ≧ StartTS is satisfied, and the frame number NFN. Is set to the start frame number FN. The above is the outline of step S105.

  If the automatic mode constant is a true / false value “N” in the process of step S103, the content acquisition unit 1021 determines whether the value of the playback state flag is a true / false value “Y” ( In step S106), if the value is a true / false value “Y”, the process proceeds to step S107. If the value is a true / false value “N”, the process proceeds to step S103.

  In the case where the value of the reproduction state flag is the true / false value “Y” in the process of step S106, or in the case of the process continued from step S105, the content acquisition unit 1021 obtains the current time obtained from the system clock oscillation unit 1023. The elapsed time is calculated from NTS, playback start time STS, and system clock frequency SS, and the transmittable range is searched by calculating sendable time information LastTS from the elapsed time, content playback time CTS, and track timestamp frequency TRS. (Step S107). The formula for calculating the sendable time information LastTS is shown below.

<Equation 3>
LastTS = (NTS−STS) / SS × TRS
Here, the system clock frequency SS is a constant for converting (current time NTS−reproduction start time STS) into seconds. For example, if the system clock has an accuracy of 1/1000000 second, it is 1000000.

  Next, the content acquisition unit 1021 sequentially searches the frame number from the start frame number FN in the track indicated by the track number TN in the content file name CF, and acquires the frame number NFN at which time information ≧ LastTS is satisfied. To do. When the frame number NFN that satisfies the condition is not found, the content acquisition unit 1021 sets the termination constant “−1” to the frame number NFN.

  Next, the content acquisition unit 1021 determines whether or not transmission is possible by comparing the start frame number FN and the frame number NFN (step S108). If FN <NFN is satisfied, the truth value “Y” is obtained. The process proceeds to S109. If not established, the truth value is “N”, and the process proceeds to Step S103.

  If the value is true or false in the process of step S108, the content acquisition unit 1021 determines that the track number TN in the track indicated by the track number TN in the content file name CF is less than the frame number NFN from the start frame number FN. For each content unit corresponding to each frame number, and for each content unit, the network time stamp PTS generated from the corresponding time information according to the following calculation formula is output to the transmission unit 1022 (step S109).

<Equation 4>
After outputting PTS = time information / TRS × network time stamp frequency, the content acquisition unit 1021 sets start frame number FN = frame number NFN to shift the start frame number FN to the transmitted position.

  If the automatic mode constant is the true / false value “Y” in the process of step S102, the content acquisition unit 1021 sets the reproduction state flag F = the true / false value “Y” and the reproduction start time STS. = The current time NTS obtained from the system clock oscillator 1023 is set, and the setting for starting automatic reproduction is performed (step S110). The above is the outline of the reproduction time management process (transmission side) of the content acquisition unit 1021.

  Next, the reproduction time management process (reception side) of the content reading unit 1034 using the network time stamp will be described with reference to the flowchart of FIG.

  When the content reading unit 1034 starts to reproduce the content, the content reading unit 1034 monitors the accumulation amount until a certain amount of content pieces are accumulated in the buffer unit 1032 (step S121), and exceeds a predetermined accumulation amount threshold value. The true / false value becomes “Y”, and the process proceeds to step S122. The threshold value of the accumulation amount may be simply half of the total buffer amount (Half Full), or when the bit rate of the content is known in advance, the buffer unit 1032 causes a buffer underflow. You may decide not to.

  Next, the content reading unit 1034 refers to the system clock oscillating unit 1033, sets the reproduction start time STS = the current time NTS obtained from the system clock oscillating unit 1023, and performs settings for starting reading (step S122). . The content reading unit 1034 sets a timeout variable TOUT = timeout constant (for example, “10”).

  Next, the content reading unit 1034 updates the current time NTS again with reference to the system clock oscillation unit 1033, and calculates the network time stamp PTS to be read according to the following calculation formula (step S123).

<Equation 5>
PTS = (NTS−STS) / SS × network time stamp frequency Next, the content reading unit 1034 searches the buffer unit 1032 based on the network time stamp PTS, and the network time stamp PTS is equal to or smaller than the network time stamp PTS. The content segment associated with is taken out (step S124). If no content fragment is found, the truth value “N” is obtained, and the content reading unit 1034 proceeds to the processing of step S125. If the content fragment is found, the truth value “Y” is obtained, and a time-out variable is set. A timeout constant (for example, “10”) is set in TOUT, and the process proceeds to step S126.

  In the case where the truth value is “N” in step S124, the content reading unit 1034 waits for a certain time (for example, about 0.5 seconds), and then subtracts the time-out variable TOUT by “1” to determine whether a time-out has occurred. Determination is made (step S125). When the subtracted TOUT is less than 0, the true / false value “Y” is obtained, and the content reading unit 1034 ends the process. When the subtracted TOUT becomes the true / false value “N”, the process proceeds to step S123. As a result, if the packet does not arrive for 5 seconds (0.5 × 10), the end operation is performed.

  If the value is true / false “Y” in step S124, the content reading unit 1034 outputs the content segment extracted in step S124 to the reproduction unit 1035 (step S126). At this time, the content pieces may be rearranged by an appropriate means so as to meet the request of the playback unit 1035, or the content pieces may be merged. For example, content pieces having the same network time stamp (RTP time stamp) may be combined after rearrangement using the sequence number in the RTP header.

  For the convenience of explanation, it was assumed that the network time stamp given to the received packet always starts from 0. However, the network time at the start of transmission is preliminarily determined by other communication procedures such as RTSP described later. When the stamp initial value OFS is known, the equation 5 can be transformed into the equation 6.

<Equation 6>
PTS = (NTS-STS) / SS x network time stamp frequency + OFS
The above is the outline of the reproduction time management process (reception side) of the content reading unit 1034 using the network time stamp.

  Next, a transmission control mechanism in the streaming system will be described.

  In a streaming system, it is necessary to select / play / stop operations such as arbitrary content from user input processing, and to dynamically connect / disconnect a session such as TCP / UDP according to the operation. This is called a transmission control mechanism. FIG. 12 shows a functional block diagram of the content distribution server 102b and the content receiving device 103b that constitute the content distribution system 101b having a transmission control mechanism. The content distribution server 102b and the content receiving device 103b are connected to each other by the IP network 104.

  The content distribution server 102b includes a content acquisition unit 1021, a transmission unit 1022, a system clock oscillation unit 1023, a content storage unit 1024, and a transmission control unit 1025. The content reception device 103b includes a reception unit 1031 and a buffer unit 1032. A system clock oscillation unit 1033, a content reading unit 1034, a reproduction unit 1035, a transmission control unit 1036, and an input unit 1037. In addition, the same number is attached | subjected about the same thing as FIG. 8, and the description is abbreviate | omitted.

  When the transmission control unit 1025 of the content distribution server 102b receives transmission control information including instructions for selecting content, playing / stopping the content, etc. from the content receiving device 103b, the transmission control unit 1025 sends the transmission control information to the content acquisition unit 1021. A function of notifying the transmission unit 1022; Also, the transmission control unit 1025 refers to the content storage unit 1024, acquires the content file name, track number, and content playback start time, inputs them to the content acquisition unit 1021, and transmits them to the transmission unit 1022 It has a function to input an address.

  The protocol to be applied is assumed to be a real-time data transmission control protocol typified by RTSP (Real Time Streaming Protocol) defined in RFC2326, and uses methods such as Setup, Play, Pause, Teardown, Describe, etc. Yes (H. Schulzrinne etal, "Real Time Streaming Protocol", RFC 2326, Internet Engineering Taskforce, Apr 1998).

  In addition, the transmission control unit 1036 of the content receiving apparatus 103b transmits the transmission control information from the input unit 1037 to the transmission control unit 1025 of the content distribution server 102b, receives the response, analyzes the response, and then extracts the reception address. , And a function of inputting to the receiving unit 1031.

  Further, the input unit 1037 of the content receiving apparatus 103b has a function of accepting transmission control information input processing such as content selection, content playback, and stop from the user. For example, using a bitmap display and a keyboard, GUI parts such as a play button, a stop button, and a content selection dialog are provided to the user.

  Next, operations of transmission control section 1025 and transmission control section 1036 at the time of transmission / reception of transmission control information will be described using the sequence diagram of FIG. FIG. 13 shows a process performed by selecting one content using RTSP, establishing a session for transmission, starting playback, and stopping. Here, the host name of the content distribution server 102b is “server.jvc-victor.jp”, the content file name storing the content is “hoge.mp4”, and “hoge.mp4” contains 1 Assume that there are two MPEG-4 AAC audio tracks, the track number is 1, and the playback time is 235 seconds.

  RTSP applies content URIs (Uniform Resource Identifiers) as resource identifiers to uniquely identify content on the network (T. Berners-Lee, "Uniform Resource Identifiers (URI): Generic Syntax", RFC2396, Internet Engineering Taskforce, Aug 1998). The content “hoge.mp4” is represented by the following content URI.

“Rtsp: //server.jvc-victor.jp/hoge.mp4”
First, the transmission control unit 1036 requests a session description using the content URI (step S131). The session description is text data indicating what kind of session (communication path) can be established for the content data associated with the content URI. As a session description format, Session Description Protocol (SDP) is applied (M. Handley, “SDP: Session Description Protocol”, RFC2327, Internet Engineering Taskforce, April 1998). Use the DESCRIBE method to request a session description in RTSP. Each method and its response message (including other accompanying information) are inserted and received in the header of the request message and the header of the response message, respectively.

“DESCRIBE rtsp: //server.jvc-victor.jp/hoge.mp4 RTSP / 1.0”
The transmission control unit 1025 transmits a response including the session description (step S132). The session description includes a playback time and a media description. This playback time is the maximum playback time of continuous media associated with the specified content URI. There are many types of playback time formats, but the simplest format is NPT (Normal Play Time, ISO8601) in which the start time and end time are expressed in seconds using floating point. For example, the reproduction time of a content URI indicating a content file including an MPEG-4 AAC audio track for 235 seconds is expressed as follows using NPT.

“A = range: npt = 0.0-235.0”
Also, the media description includes information such as content type and network time stamp frequency as prior information for establishing a session.

“M = audio 0 RTP / AVP / UDP 96”
“A = rtpmap: 96 mpeg4-generic / 48000/2”
“A = control: rtsp: //server.jvc-victor.jp/hoge.mp4/trackID=1”
“A = fmtp: 96 streamtype = 5; profile-level-id = 15; mode = AAC-hbr; config = 1190; SizeLength = 13; IndexLength = 3; IndexDeltaLength = 3; Profile = 1;”
The above media description expresses that stereo sound of 48000 Hz (48 KHz) PCM sample frequency encoded by the MPEG-4 AAC Hi-bitrate encoding method is included. Also, it is shown that when establishing a session, UDP must be used as a lower layer network protocol and RTP should be applied for transmission.

  Also, it is shown that the following control URI is used for the preparation request of this session. The control URI is given a track number (trackID = 1) to identify a plurality of tracks in one content data.

“Rtsp: //server.jvc-victor.jp/hoge.mp4/trackID=1”
After analyzing the session description, the transmission control unit 1036 determines to establish a session for transmitting MPEG-4 AAC stereo audio, determines a reception address of the session, and transmits a session establishment preparation request to the transmission control unit 1025. (Step S133). The SETUP method is used for a session establishment preparation request in RTSP. In the following example, the reception address is the reception address (136.198.190.100) and the reception port number (6668-6669) that the transmission control unit 1036 has.

“SETUP rtsp: //server.jvc-victor.jp/hoge.mp4/trackID=1 RTSP / 1.0”
“Transport: RTP / AVP / UDP; unicast; destination = 136.198.190.100; client_port
= 6668-6669 ”
Upon receiving the session establishment preparation request correctly, the transmission control unit 1025 newly determines a transmission address, inputs the transmission address to the transmission unit 1022, and transmits session information to the transmission control unit 1036 (step S134). The session information includes a transmission address (136.198.190.1 in the example) and a transmission port number (19000 to 19001 in the following example) used for distribution.

“Transport: RTP / AVP / UDP; unicast; source = 136.198.190.1; server_port = 19000
-19001 ”
In addition, the transmission control unit 1036 inputs the previously determined reception address to the reception unit 1031 when the session information is received. A new session is established when the processing of both the transmission unit 1022 and the reception unit 1031 is completed.

  Next, the transmission control unit 1036 transmits a reproduction start request (step S135). In the playback start request, the playback range can be specified using NPT. In the example below, the content is specified from the beginning (0.0 seconds) to the end (235.0 seconds). The PLAY method is used for a playback start request in RTSP.

“PLAY rtsp: //server.jvc-victor.jp/hoge.mp4 RTSP / 1.0”
“Range: npt = 0.0-235.0”
The transmission control unit 1025 transmits a response to the reproduction start request (step S136). The transmission control unit 1025 that has received the reproduction start request, for all the sessions that have already been prepared, from the control URI of each session and the reproduction range included in the reproduction start request, the content file name / track number / content reproduction start The time is calculated and input to the content acquisition unit 1021 together with command input = reproduction start constant (eg, “PLAY”), and transmission of the RTP packet is started.

  This response also includes RTP packet information necessary for the operation of the content reading unit 1034 of the content receiving device 103b. For example, in this session, the RTP time stamp (network time stamp) of the first RTP packet sent is included (0000000 in the following example).

“RTP-Info: url = rtsp: //server.jvc-victor.jp/hoge.mp4/trackID=1; rtptime
= 0000000; ”
The transmission control unit 1036 transmits a stop request when the user makes a stop input (step S137). In RTSP, the stop request is the TEARDOWN method.

“TEARDOWN rtsp: //server.jvc-victor.jp/hoge.mp4 RTSP / 1.0”
The transmission control unit 1025 that has received the stop request controls the transmission unit 1022 to stop the transmission of the RTP packet, disconnect the session, and notify that the transmission is stopped (step S138). In addition, the transmission control unit 1025 inputs command input = reproduction stop constant (for example, “STOP”) to the content acquisition unit 1021 and stops reading.

  For simplification of explanation, it is assumed that only one content is included in one content data. However, the transmission control mechanism can be easily extended to synchronous reproduction of a plurality of contents. For example, it is possible to easily perform synchronized playback of a plurality of contents simply by listing media descriptions regarding a plurality of contents in step S132 and repeating the preparation requests in steps S133 to S134 for the media descriptions. The above is the outline of the transmission control mechanism in the streaming system.

  Here, when trying to switch between audio and video dynamically and smoothly during content playback, a streaming system employing an asynchronous model and a streaming system equipped with a transmission control mechanism with dynamic session generation Therefore, it is not possible to smoothly perform the bitstream switching operation from the middle of reproduction of two or more contents.

  For example, out of two contents (track numbers 1 and 2) having a playback time of 235 seconds, the content of track number 1 is being played back, and the user moves to the content of track number 2 in the 100th second. It is assumed that a switching instruction is input to the input unit 1037.

  Since the content receiving apparatus 103b employs an asynchronous model, the 100th second seen from the user is a time difference (current time NTS−reproduction start time STS) calculated inside the content reading unit 1034. In the buffer unit 1032, the content pieces after the 100th second already transmitted from the content distribution server 102 b have already been accumulated, or a part of them has stayed in the router or switching hub on the IP network 104. it is conceivable that.

  In this situation, when the session of track number 1 is disconnected (step S137) and a series of communication procedures from step S133 to step S135 are performed on the content of track number 2, the reproduction range in step S135 is as follows. It must be specified like this.

“PLAY rtsp: //server.jvc-victor.jp/hoge.mp4 RTSP / 1.0”
“Range: npt = 100.0-235.0”
FIG. 14 shows a permutation of content pieces stored in the buffer unit 1032 immediately after the process of step S136. Let T1 be the time information of content with a playback time of 100 seconds, and T2, T3, and T4 in chronological order. FIG. 14 shows that the content of track number 1 is accumulated up to the content segment 4, and subsequently the content of track number 2 is accumulated from the content segment 1. When the user views in this permutation of content pieces, the content returns from T4 to T1, so it feels like it has been wound for a moment, and it does not switch smoothly, and a severe discomfort occurs.

The time taken from the time when the session with track number 1 is disconnected in the process of step S137 until the request for preparation for session establishment with track number 2 is received is the total playback time of packets already accumulated in the buffer unit 1032. If it is longer than this, a buffer underflow occurs, and when the timeout variable TOUT of the content reading unit 1034 expires, the reproduction stops.
Similarly, the session of track number 1 is disconnected in the process of step S137, the time taken for a series of communication procedures from step S133 to step S135 is measured for the content of track number 2, and the track number in the process of step S135 is measured. A method to reduce the sense of incongruity by correcting the NPT of 2 can be considered. For example, if it takes 5.5 seconds for a series of communication procedures, it is corrected to npt = 105.5-235.0.

  However, even if this method is applied, it is not possible to consider the time delay until the reproduction start request for track number 2 reaches the content distribution server 102b and the packet transmission is actually started. It is difficult to configure the content playback time for packets to be completely continuous.

  Japanese Patent Laid-Open No. 2002-118592 (Patent Document 1) is disclosed as a first improvement method for coping with the above problem.

  This is because a secondary delivery server is provided between the delivery server and the client, and the secondary delivery server buffers the bitstream after switching to some extent and then switches, so that the client buffer is not emptied and the content is It can be switched without interruption.

  However, in Patent Document 1, each of bitstreams distributed from a plurality of distribution servers is temporally independent from each other, and frame boundaries are not synchronized. That is, buffer underflow can be prevented, but the content rewinding feeling is ineffective, and it is difficult to configure the content playback time to be completely continuous.

  As a second improvement method for coping with the above problem, many streaming systems adopt a multi-track simultaneous reception configuration. As an example, FIG. 15 shows a functional block diagram of the content distribution server 102c and the content reception device 103c that constitute the content distribution system 101c capable of receiving two tracks simultaneously.

  The content distribution server 102c includes a content acquisition unit 1021A, a transmission unit 1022A, a content acquisition unit 1021B, a transmission unit 1022B, a system clock oscillation unit 1023, and a content storage unit 1024. In addition, the content receiving device 103c includes a receiving unit 1031A, a buffer unit 1032A, a content reading unit 1034A, a receiving unit 1031B, a buffer unit 1032B, a content reading unit 1034B, a system clock oscillation unit 1033, a reproduction unit 1035, a transmission control unit 1036, an input Part 1037 and switching part 1038. In addition, the same number is attached | subjected about the same thing as FIG. 12, and the description is abbreviate | omitted.

  The switching unit 1038 has a function of adopting one of the two content segments and inputting it to the playback unit 1035 in accordance with the track switching input. Although the content piece that has not been adopted is read, it is discarded as it is.

  Note that the input unit 1037 accepts a track switching input for switching the track number 1 or 2 input by the user.

  When there are a plurality of synchronized tracks, the content receiving apparatus 103c repeats a series of preparation requests / responses corresponding to steps S133 to S134 for the number of tracks, and then starts a reproduction request corresponding to step S135. This is dealt with by providing the content receiving apparatus 103c with a switching unit 1038 that receives a stream corresponding to the number of tracks and reproduces one of a plurality of tracks on the receiving side.

  FIG. 16 is a flowchart showing the operation of the content receiving apparatus 103c having a multiple-track simultaneous reception configuration. Since all the processes (steps S142 to S146) other than the process of step S141 are the same as steps S122 to S126 of FIG.

  In order for a plurality of tracks to synchronize with each other, it is necessary to start reproduction all at once without depending on a slight difference in the accumulation amount of the buffer unit (time fluctuation of the reproduction content pieces that arrive). Therefore, the content reading unit 1034 (A or B) on the side that receives the content of the track that is selected for playback monitors all the buffer units 1032 (A and B) in the content receiving device 103c and accumulates a certain amount. If any one of the buffer units exceeds a predetermined accumulation amount threshold value, a true / false value “Y” is generated and the process proceeds to the next process (step S141). In other words, it is intended that the reproduction start times STS between a plurality of tracks are exactly the same.

  Conventionally, content was distributed in this way, but had the following problems.

  First, the secondary distribution server of Patent Document 1 can switch bitstreams for transmitting a plurality of contents transmitted from a plurality of distribution servers and provide them to clients, but has a synchronization clock shared by each distribution server. In addition, since the bit stream constituted by the packets with the same network time stamp added at the same time is not transmitted, the increment of the content reproduction time in the content cannot be completely matched and switched smoothly.

  Further, the content distribution system 101 configured to receive multiple tracks simultaneously has the following problems.

  In the content distribution systems 101b and 101c shown in FIGS. 12 and 15, a network throughput exceeding the sum of the bit rates of the tracks is required. For example, if there are 20 128 Kbps MPEG-4 AAC audio tracks, the required network throughput is 20 times 2.5 Mbps. In particular, when a relatively low-speed communication line using a wireless network is used, there is a possibility that the throughput becomes insufficient and the service becomes impossible.

In particular, the content receiving apparatus 103c in FIG. 15 needs to include as many buffer units (1032A and 1032B in FIG. 15) as the number of tracks. Further, since the content receiving apparatus 103c employs an asynchronous model, it is necessary to increase the storage capacity of the buffer unit in order to simultaneously receive and manage different bit streams. In particular, when a device having a limited amount of memory, such as a mobile phone or a PDA (Personal Digital Assistant = portable information terminal), is used as a content receiving device, it may not be mounted.
JP 2002-118592 A

  The present invention has been made in view of the above circumstances, and a content distribution system comprising a content distribution server that transmits content data composed of a plurality of tracks via a network, and a content reception device that receives and reproduces the content data. The present invention relates to a content distribution method, a content distribution server using the content distribution method, and a content receiving apparatus that can dynamically switch and transmit tracks and smoothly reproduce the switched portion.

  In order to achieve the above object, a content distribution method according to claim 1 includes a content distribution server storing content data having a plurality of content segment data, and the content distribution server via a network. A content distribution method in a content distribution system comprising: a content reception device that requests content reproduction and receives and reproduces content fragment data transmitted from the content distribution server via the network in response to the reproduction request. The content data stored in the content distribution server is content data having a file name and a plurality of tracks, and the track data of each track has a track number and a plurality of data frames. Data frame, frame number, playback Time information indicating timing and content fragment data, and the data frames of the respective tracks in the same frame number have the same time information, and the content distribution from the content receiving device The file name of the content data requesting reproduction is transmitted to a server, and at least the track number set in advance transmitted from the content distribution server in response to the file name, and the preset in the content data of the file name The content reception device receives the reproduction time information indicating the reproduction time length of the track of the track number being set, and the content reception device designates the desired track number and transmits it to the content distribution server, thereby Content receiver-front A session establishing step for establishing a session between content distribution servers, and when making a content reproduction start request after the establishment of the session, the file name of the content data requesting the reproduction in the content receiving device, and A step of transmitting a content reproduction start request message including reproduction range information indicating a reproduction time range from the content receiving device to the content distribution server, and when the content distribution server receives the reproduction start request message. The frame number of the data frame including the content fragment data to be transmitted is identified according to the reproduction range information in the reproduction start request message, and the identified frame number and the reproduction start request message The file name, And obtaining the content fragment data requested to be played, which is designated by the track number designated by the content receiving device when the session is established, from the stored content data, and transmitting the content piece data to the content receiving device; When the playback request track switching request is made after the session is established, the content receiving device sends a switching request message including a switching destination track number for switching the playback track from the content receiving device to the content distribution server. And when the switching request message is received after receiving the playback start request message in the content distribution server, the playback order of the content piece data already sent at the time when the switching request message is received Is the last Based on the time information in the data frame including the content fragment data, the data frame including the content fragment data to be reproduced continuously with the content fragment data whose reproduction order is last. A frame number is specified, and the content fragment data specified by the specified frame number and the switching destination track number in the switching request message is acquired from the stored content data, and content reception is performed. And transmitting to the apparatus.

  In the present invention, “content segment data” refers to a data block obtained by dividing content by an arbitrary data length.

  The content distribution server according to claim 2 selects content fragment data requested to be reproduced from content data having a plurality of content fragment data in accordance with a reproduction request from the content receiving device, and selects the selected content fragment. A content distribution server for transmitting data to the content receiving device via a network, wherein the content data has a file name and a plurality of tracks. The track data of each track includes a track number, a plurality of data frames, And each data frame has a frame number, time information indicating reproduction timing, and content fragment data, and the data frames of the tracks in the same frame number have the same time. Store content data with information And receiving the file name of the content data to be reproduced from the content storage means and the content receiving device, and at least the track number set in advance according to the file name and the preset in the content data of the file name The content receiving apparatus transmits the reproduction time information indicating the reproduction time length of the track of the track number being set to the content receiving apparatus, and then receives the desired track number designated by the content receiving apparatus. A session with the content data, and after the establishment of the session, when a content playback request is made in the content receiving device, the content receiving device requests the file name of the content data to be played back, and Indicates the time range to play When a content playback start request message is received including content range information and the session is established in the content receiving device after the session is established, the content receiving device switches the playback track. A transmission control unit for receiving a switching request message including a switching destination track number; and when the transmission control unit receives the reproduction start request message, the transmission control unit transmits the switching request message according to the reproduction range information in the reproduction start request message. The frame number of the data frame including the content fragment data to be identified is identified, and the identified frame number, the file name in the reproduction start request message, and the content receiving device specified when the session is established Playback required specified by the track number When the content fragment data of the obtained content is acquired from the content storage means, and when the transmission control means receives the switching request message after receiving the reproduction start request message, the time when the switching request message is received Based on the time information in the data frame including the content segment data whose playback order is the last among the content segment data already sent in the above, the content segment whose playback order is the last The frame number of the data frame including the content fragment data to be continuously reproduced in the data is specified, and is specified by the specified frame number and the switching destination track number in the switching request message. The content segment data from the content storage means A content obtaining means for obtaining, and a sending means for sending the content fragment data which the content acquisition unit has acquired to the content receiving apparatus.

In addition, the content receiving device according to claim 3 makes a content reproduction request via a network to a content distribution server that stores content data having a plurality of content segment data, and responds to the reproduction request. In response, the content receiving apparatus receives and plays back the content fragment data transmitted from the content distribution server via the network, and the content data stored in the content distribution server includes a file name and a plurality of tracks. The track data of each track has a track number and a plurality of data frames, and each data frame has a frame number, time information indicating reproduction timing, and content fragment data. At the same frame number. The data frame of each track has the same time information, transmits the file name of the content data requesting reproduction, and is transmitted at least in advance from the content distribution server accordingly. Receiving the playback time information indicating the playback time length of the track having the preset track number in the content data having the track number and the file name, and then specifying the desired track number to specify the content By establishing a session with the content distribution server by transmitting to the distribution server, and when making a content reproduction start request after the session has been established, the file name of the content data that requests reproduction, and Content containing playback range information indicating the time range to be played When a playback start request message is transmitted to the content distribution server and a switching request for a playback target track is made after the session is established, a switching request message including a switching destination track number for switching the playback track is sent to the content distribution server. In the transmission control means for transmitting and the content distribution server, when the switching request message is received after receiving the reproduction start request message, the content piece data already sent at the time of receiving the switching request message Based on the time information in the data frame including the content segment data whose playback order is last, the content segment to be played back continuously with the content segment data whose playback order is last The frame number of the data frame including fragment data And receiving means for receiving the content fragment data specified and transmitted by the specified frame number and the switching destination track number in the switching request message from the content distribution server. It is characterized by.

  According to the present invention, the content distribution server side acquires and transmits the data frame by matching the reproduction time information of the data frame at the track switching location, so that the content receiving device can smoothly reproduce the track switching location. It becomes possible. In particular, when the content data of each track is highly related to the temporal transition (for example, when the same song is sung in Japanese and English), the track is switched. It becomes possible to reproduce the portion very smoothly.

  Further, since there is no need to transmit redundant data frames to the content receiving device, it is possible to reduce the manufacturing cost of the content receiving device without requiring a buffer memory for storing a large amount of data frames on the content receiving device side. Become. Further, since only one communication line is exclusively used for data frame transmission, it is possible to provide a good service even with a low-throughput communication line.

  An embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 shows a functional block diagram of the content distribution server 2 and the content receiving device 3a in the content distribution system 1a (asynchronous model). The content distribution server 2 and the content receiving device 3a are connected to each other by the IP network 4.

  The content distribution server 2 includes a content acquisition unit 21, a transmission control unit 22, a transmission unit 23, a system clock oscillation unit 24, and a content storage unit 25.

  The content acquisition unit 21 records content data of the content to be reproduced in the content storage unit 25, and acquires a content fragment using an arbitrary pointer (read position on the content) based on the transmission control information in accordance with the system clock signal. It has the function to do. This pointer is any one of the content file name, the track number, and the frame number, or some combination thereof. The “content segment” refers to a data block having an arbitrary data length.

  The content acquisition unit 21 has initial values such as a content file name, a track number, and a frame number inside, and may automatically start reading from the time of start-up, or the content file name, track number, and content from an external input Reading may be started after the reproduction start time is obtained. Further, an external input for receiving command input is provided, and when command input = reproduction start constant (for example, “PLAY”), reproduction may be performed, or command input = reproduction stop constant (for example, “STOP”). If so, it may be stopped. Alternatively, the automatic read start operation and the external read start operation may be automatically determined.

  When the transmission control unit 22 receives transmission control information including instructions such as content selection, content playback / stop, and track switching request from the content receiving device 3b, the transmission control unit 22 transmits the transmission control information to the content acquisition unit 21. The function of notifying the unit 23 is provided. Also, the transmission control unit 22 refers to the content storage unit 25 to acquire the content file name, track number, and content playback start time, inputs them to the content acquisition unit 21, and transmits them to the transmission unit 23. It has a function to input an address.

  As a protocol to be applied, a real-time data transmission control protocol typified by RTSP defined in RFC2326 is assumed, and methods such as Setup, Play, Pause, Teardown, and Describe can be used.

  The transmission unit 23 has a function of securing a virtual communication path called a session, packetizing the content fragment with an appropriate header, and transmitting the packet to the content reception device 3a via the IP network 4. Have. For example, the header includes a network time stamp.

  When transmitting a packet, the transmission unit 23 uses a transmission address to deliver the packet to the content receiving device 3a. The transmission address is composed of a combination of a transmission address and a transmission port number. The transmission address may be previously stored as a constant in the transmission unit 23, or an input may be received from another block. Note that a session (communication path) for transmitting a packet is dynamically established when a transmission address is determined. Further, the content segment and the packet do not necessarily match.

  The system clock oscillator 24 is a real-time clock (high-precision clock) realized by a crystal oscillator or the like, and has a function of supplying a system clock signal to the content acquisition unit 21.

  The content storage unit 25 has a function of storing content data in a predetermined file format.

  In addition, the content receiving device 3 a includes a receiving unit 31, a transmission control unit 32, a buffer unit 33, a system clock oscillation unit 34, a content reading unit 35, a playback unit 36, and an input unit 37.

  The receiving unit 31 has a function of receiving a packet from the IP network 4, interpreting the header, taking out a content fragment, and supplying it to the buffer unit 33. The receiving unit 31 uses the reception address in order to receive only packets necessary for itself among the packets from the content distribution server 2. The reception address is composed of a combination of a reception address and a reception port number. The reception address may be previously stored as a constant inside the reception unit 31, or input may be received from another block.

  The transmission control unit 32 has a function of transmitting the transmission control information from the input unit 37 to the transmission control unit of the content distribution server 2, receiving the response, analyzing the response, extracting the reception address, and inputting the received address to the reception unit 31. Have

  The buffer unit 33 has a function of temporarily accumulating and storing the content pieces together with a network time stamp (described later) obtained from the header.

  The content reading unit 35 monitors the buffer unit 33 and starts reading the content unit in accordance with the system clock signal from the system clock oscillation unit 34 when it is determined that the content unit sufficient for reproduction has been accumulated. It has a function of restoring and outputting a set of segments as content.

  The playback unit 36 has a function of performing decoding according to the input content segment and outputting an audio signal and a video signal to a predetermined output device such as a speaker. For example, when the content segment is digital audio data encoded with high efficiency similar to MPEG, the playback unit 36 includes a high efficiency code decoder (decoder), a D / A converter, an analog amplifier, and the like. Is done.

  The input unit 37 has a function of accepting transmission control information input processing such as content selection, content playback / stop, and track switching from the user. For example, using a bitmap display and a keyboard, GUI parts such as a play button, a stop button, and a content selection dialog are provided to the user, and a track number is input using a numeric keypad and several stages of slide switches. Provide an operation switch that accepts.

  Next, the data structure of content data in this embodiment will be described.

  The feature of the bitstream switching method according to the present embodiment is that when a track switching request is input and the track is switched, the start frame number FN that has scanned the track before switching is used as it is, so that the before and after switching The content playback time is in a completely continuous form (details will be described later).

  Basically, like the conventional content data shown in FIG. 9, the content data in this embodiment is composed of a content file name, the total number of tracks T, and track data of each track, and further, track data of each track. Is composed of a track number, a track time stamp frequency, the total number of frames, and a plurality of data frames, and each data frame is composed of a frame number, time information, and a content fragment.

  Content pieces for a plurality of tracks are received from the content distribution server 2 while the receiving unit 31, the buffer unit 33, the content reading unit 35, and the playback unit 36 of the content receiving device 3a are not changed from the conventional ones. In order to continue the reproduction smoothly when reaching the receiving device 3a, at least the content reproduction time in each data frame in which the content segment is assigned to the plurality of tracks that can be switched in the content file. The above temporal boundaries must match (content pieces having the same frame number are played back at the same playback time).

  In other words, when the same frame numbers FNA and FNB exist in a certain track A and a certain track B, the time information accompanying the FNA / track time stamp frequency of the track A and the time information accompanying the FNB / the time information of the track A The track timestamp frequency must match.

  FIG. 2 shows a data structure of content data having a plurality of tracks (arranged along the time axis). The horizontal axis represents the content playback time (each time information / track time stamp frequency).

  In FIG. 2, content pieces, FN1, FN2,... FNn, FNm, etc. are frame numbers assigned to the content pieces. The total number of frame numbers of one track does not need to match, and in FIG. 2, track 1 has a total number of frames n and track 2 has a total number of frames m. If the content data has been subjected to high-efficiency encoding such as MPEG-4 AAC hi-bitrate encoding, a single content segment includes a plurality of high-efficiency encoded compressed packets. It doesn't matter.

  However, the total time length when reproducing a plurality of compressed packets included in one content segment must match when content segments having the same frame number are extracted from two or more tracks. Therefore, the time information x of the content segment x of each track in the same frame number FNx always has the same value if the track timestamp frequency of each track is the same value.

  Therefore, as indicated by an arrow (A) in FIG. 2, even if the frame number FN2 is switched from the track 1 to the track 2 during the reproduction, the reproduction can be continued smoothly.

  Next, operations of the transmission control unit 22 of the content distribution server 2 and the transmission control unit 32 of the content receiving device 3a at the time of transmission / reception of transmission control information will be described with reference to the sequence diagram of FIG. FIG. 2 shows a process performed until one content is selected using RTSP, a session for transmission is established, playback is started, and stopped. Included in the information.

  Here, the host name of the content distribution server 2 is “server.jvc-victor.jp”, the content file name that stores the content is “hoge.mp4”, and “hoge.mp4” contains 1 Assume that there are two MPEG-4 AAC audio tracks, the track number is 1, and the playback time is 235 seconds.

  RTSP applies the content URI as a resource identifier for uniquely identifying the content on the network. The content “hoge.mp4” is represented by the following content URI.

“Rtsp: //server.jvc-victor.jp/hoge.mp4”
First, the transmission control unit 32 requests a session description using the content URI (step S01). This session description is text indicating what kind of session (communication path) can be established for the content data associated with the content URI. SDP is applied as the session description format. Use the DESCRIBE method to request a session description in RTSP. Each method and its response message (including other accompanying information) are inserted and received in the header of the request message and the header of the response message, respectively.

“DESCRIBE rtsp: //server.jvc-victor.jp/hoge.mp4 RTSP / 1.0”
The transmission control unit 22 transmits a response including the session description (step S02). The session description includes a playback time and a media description. This playback time is the maximum playback time length of continuous media associated with the specified content URI. There are many different playback time formats, but the simplest format is NPT, which represents the start time and end time in seconds using floating point. For example, the playback time of a content URI indicating content data including an MPEG-4 AAC audio track for 235 seconds is expressed as follows using NPT.

“A = range: npt = 0.0-235.0”
Also, the media description includes information such as content type and network time stamp frequency as prior information for establishing a session.

“M = audio 0 RTP / AVP / UDP 96”
“A = rtpmap: 96 mpeg4-generic / 48000/2”
“A = control: rtsp: //server.jvc-victor.jp/hoge.mp4/trackID=1”
“A = fmtp: 96 streamtype = 5; profile-level-id = 15; mode = AAC-hbr; config = 1190; SizeLength = 13; IndexLength = 3; IndexDeltaLength = 3; Profile = 1;”
The above media description expresses that stereo sound of 48000 Hz (48 KHz) PCM sample frequency encoded by the MPEG-4 AAC Hi-bitrate encoding method is included. Also, it is shown that when establishing a session, UDP must be used as a lower layer network protocol and RTP should be applied for transmission.

  Also, it is shown that the following control URI is used for the preparation request of this session. The control URI is given a track number (trackID = 1) to identify a plurality of tracks in one content data.

“Rtsp: //server.jvc-victor.jp/hoge.mp4/trackID=1”
The transmission control unit 32 that has analyzed the session description determines a reception address of the session and transmits a session establishment preparation request to the transmission control unit 22 in order to establish a session for transmitting MPEG-4 AAC stereo audio ( Step S03). The SETUP method is used for a session establishment preparation request in RTSP. In the following example, the reception address is the reception address (136.198.190.100) and the reception port number (6668-6669) that the transmission control unit 32 has.

“SETUP rtsp: //server.jvc-victor.jp/hoge.mp4/trackID=1 RTSP / 1.0”
“Transport: RTP / AVP / UDP; unicast; destination = 136.198.190.100; client_port
= 6668-6669 ”
The transmission control unit 22 that has correctly received the session establishment preparation request newly determines a transmission address, inputs the transmission address to the transmission unit 23, and transmits session information to the transmission control unit 32 (step S04). The session information includes a transmission address (136.198.190.1 in the example) and a transmission port number (19000 to 19001 in the following example) used for distribution.

“Transport: RTP / AVP / UDP; unicast; source = 136.198.190.1; server_port = 19000
-19001 ”
Further, the transmission control unit 32 inputs the previously determined reception address to the reception unit 31 when the session information is received. A new session is established when the processing of both the transmission unit 23 and the reception unit 31 is completed.

  Next, the transmission control unit 32 transmits to the transmission control unit 22 a track switching request (CHANGE method) for designating a track of content to be played in accordance with a user's input operation (step S05). In the track number designation (TrackID =), the track number to be switched next is set.

“CHANGE rtsp: //server.jvc-victor.jp/hoge.mp4/TrackID=2 RTSP / 1.0”
Upon receiving the track switching request, the transmission control unit 22 refers to the content storage unit 25, and when the track corresponding to the track number to be switched next exists in the content hoge.mp4, transmits the following normal response (Step S06).

“RTSP / 1.0 200 OK”
If the track corresponding to the track number to be switched next does not exist in the content hoge.mp4, the transmission control unit 22 transmits the following abnormal response.

“RTSP / 1.0 404 NOT FOUND”
Note that the track switching request and the track switching response are examples, and uniqueness is not lost due to a slight difference in the character string expression. RTSP has been expanded this time, but using the HTTP (Hyper Text Transfer Protocol) GET method, the track switching request may be rewritten as follows (Network Working Group, "Hypertext Transfer Protocol-HTTP / 1.1" , RFC2616, The Internet Society, June 1999).

“GET /hoge.mp4?TrackID=2 HTTP / 1.1”
Although the host name of the content distribution server 22 is not included in the GET method, the content file name and the track number to be switched next can be included in the same manner as RTSP.

  Next, the transmission control unit 32 transmits a reproduction start request (step S07). In the playback start request, the playback range can be specified using NPT. In the example below, the playback range is specified from the beginning (0.0 seconds) to the end (235.0 seconds) of the content. The PLAY method is used for a playback start request in RTSP.

“PLAY rtsp: //server.jvc-victor.jp/hoge.mp4 RTSP / 1.0”
“Range: npt = 0.0-235.0”
The transmission control unit 22 transmits a response to the reproduction start request (step S08). The transmission control unit 22 that has received the playback start request, for all sessions already prepared, starts the content file name / track number / content playback start from the control URI of each session and the playback range included in the playback start request. The time is calculated and input to the content acquisition unit 21 together with command input = reproduction start constant (eg, “PLAY”), and transmission of the RTP packet is started.

  This response includes RTP packet information necessary for the operation of the content reading unit 35 of the content receiving device 3a. For example, in this session, the RTP time stamp (network time stamp) of the first RTP packet sent is included (0000000 in the following example).

“RTP-Info: url = rtsp: //server.jvc-victor.jp/hoge.mp4/trackID=1; rtptime
= 0000000; ”
The track switching request may be transmitted anytime after the preparation request response in step S04 and before the stop. Accordingly, when track switching is input during playback of a certain track, the transmission control unit 32 transmits the track switching request transmitted in step S05 (step S09), and the transmission control unit 22 receives the track switching request. Then, the track number to be switched next is input to the content acquisition unit 21. The content acquisition unit 21 confirms the presence of the track number to be switched next, and inputs the switching result (= normal or = abnormal) to the transmission control unit 22. When the switching result is input, the transmission control unit 22 transmits a track switching response (a normal response if the switching result = normal, an abnormal response if the switching result = abnormal) to the transmission control unit 32 (step S10). ).

  Further, the content acquisition unit 21 acquires a content fragment of the designated track from the content storage unit 25 and transmits it to the content reception device 3a via the transmission unit 23 (details will be described later).

  Moreover, the transmission control part 32 transmits a stop request | requirement at the time of a user performing stop input (step S11). In RTSP, the stop request is the TEARDOWN method.

“TEARDOWN rtsp: //server.jvc-victor.jp/hoge.mp4 RTSP / 1.0”
The transmission control unit 22 that has received the stop request controls the transmission unit 23 to stop transmission of the RTP packet, disconnect the session, and notify that the transmission has been stopped (step S12). Further, the transmission control unit 22 inputs command input = reproduction stop constant (for example, “STOP”) to the content acquisition unit 21 and stops reading.

  For simplification of explanation, it is assumed that only one content is included in one content data. However, the transmission control mechanism can be easily extended to synchronous reproduction of a plurality of contents. For example, it is possible to easily perform synchronized playback of a plurality of contents simply by listing media descriptions regarding a plurality of contents in step S02 and repeating the preparation requests in steps S03 to S04 for the media descriptions.

  Next, the reproduction time management process (transmission side) of the content acquisition unit 21 when reading content data will be described with reference to the flowchart of FIG.

  First, when a content reproduction request is made from the content receiving device 3a, the content acquisition unit 21 of the content distribution server 2 initializes the following six variables (step S21).

1: Content file name CF = Default content file name (eg "hoge.mp4")
2: Track number TN = default track number (eg "1")
3: Start frame number FN = default frame number (for example, “1”)
4: Playback start time STS = current time NTS obtained from the system clock oscillator 24
5: Content playback time CTS = “0”
6: Playback state flag F = true value “N”
Next, the content acquisition unit 21 refers to a predetermined automatic mode constant indicating whether or not to automatically start reproduction, and determines whether to perform automatic reproduction (step S22). If the automatic mode constant is a true / false value “Y”, the process proceeds to step S34. If the automatic mode constant is a true / false value “N”, the process proceeds to step S23.

  In the process of step S22, when the constant is a true / false value “N”, the content acquisition unit 21 performs external input (command input CMD, content file name CF1, track number TN1, content reproduction start time CTS1 4). If there is an external input, the true value is “Y” and the process proceeds to step S24. If there is no external input, the true value is “N”. The process proceeds to step S30.

  In the process of step S23, when the value is “Y”, the content acquisition unit 21 determines whether command input CMD = track switching constant (for example, “CHANGE”) among external inputs (step S23). S24) If it is a track switching constant, the true / false value is “Y”, and the process proceeds to step S25. If the true / false value is “N”, the process proceeds to step S28.

  Also, in the process of step S24, if the truth value is “Y”, the content acquisition unit 21 uses (content file name CF1, track number TN1) among the external inputs, and CF and CF1 are equal. In addition, it is determined whether the track indicated by the track number TN1 exists in the content file name CF and whether the track can be switched (step S25). If it is possible, the true value becomes “Y” and the process proceeds to step S26. After substituting TN = track number TN1 and performing track switching processing, the transmission control unit 22 is notified of the switching result = normal (step S26). If the track is not present and cannot be switched, the truth value “N” is obtained, and the content acquisition unit 21 proceeds to the process of step S27 and notifies the transmission control unit 22 of the switching result = abnormal (step). S27).

  In the process of step S24, when the truth value is “N”, the content acquisition unit 21 determines whether command input CMD = reproduction stop constant among external inputs (step S28), and the command If the input CMD = reproduction stop constant, the truth value “Y” is obtained, and the entire operation is stopped. Otherwise, the truth value “N” is obtained, and the process proceeds to step S29.

  In the process of step S28, when the truth value is “N”, the content acquisition unit 21 uses three variables of external input (content file name CF1, track number TN1, content playback start time CTS1), First, five variables are initialized (step S29).

1: Content file name CF = Content file name CF1
2: Track number TN = Track number TN1
3: Playback start time STS = current time NTS obtained from the system clock oscillator 24
4: Content playback time CTS = Content playback start time CTS1
5: Playback state flag F = true value “Y”
Subsequently, the content acquisition unit 21 initializes the start frame number FN using the content reproduction time CTS, and calculates transmission start time information StartTS as a previous step. The calculation formula of the transmission start time information StartTS is shown below.

<Equation 7>
StartTS = CTS × TRS
Here, the track time stamp frequency TRS is the track time stamp frequency of the track indicated by the track number TN in the content file name CF.

  Next, the content acquisition unit 21 searches the frame number of the track indicated by the track number TN in the content file name CF in order from 1 to obtain the frame number NFN of the point where time information ≧ StartTS is satisfied, and the frame number NFN. Is set to the start frame number FN. The above is the outline of step S29.

  If the automatic mode constant is the true / false value “N” in the process of step S23, the content acquisition unit 21 determines whether or not the value of the playback state flag is the true / false value “Y” ( If the value is a true / false value “Y”, the process proceeds to step S31, and if the value is a true / false value “N”, the process proceeds to step S23.

  In the case where the value of the playback state flag is the true / false value “Y” in the process of step S30, or in the case of the process that continues from steps S26, S27, and S29, the content acquisition unit 21 starts from the system clock oscillator 24. Transmission is possible by calculating the elapsed time from the obtained current time NTS, playback start time STS, and system clock frequency SS, and calculating sendable time information LastTS from the elapsed time, content playback time CTS, and track time stamp frequency TRS A range is searched (step S31). The formula for calculating the sendable time information LastTS is shown below.

<Equation 8>
LastTS = (NTS−STS) / SS × TRS
Here, the system clock frequency SS is a constant for converting (current time NTS−reproduction start time STS) into seconds. For example, if the system clock has an accuracy of 1/1000000 second, it is 1000000.

  Next, the content acquisition unit 21 sequentially searches the frame number from the start frame number FN in the track indicated by the track number TN in the content file name CF, and acquires the frame number NFN at which time information ≧ LastTS is satisfied. To do. When the frame number NFN that satisfies the condition is not found, the content acquisition unit 21 sets the termination constant “−1” to the frame number NFN.

  Next, the content acquisition unit 21 determines whether or not transmission is possible by comparing the start frame number FN and the frame number NFN (step S32). If FN <NFN is satisfied, the true / false value “Y” is obtained. The process proceeds to S33. If not established, the truth value is “N”, and the process proceeds to Step S23.

  If the value in the process of step S32 is a true value “Y”, the content acquisition unit 21 is less than the frame number NFN from the start frame number FN in the track indicated by the track number TN in the content file name CF. Each content unit corresponding to each frame number and the network time stamp PTS generated according to the following calculation formula from the corresponding time information for each content unit are output to the transmission unit 23 (step S33).

<Equation 9>
After outputting PTS = time information / TRS × network time stamp frequency, the content acquisition unit 21 sets start frame number FN = frame number NFN to shift the start frame number FN to the transmitted position.

  If the automatic mode constant is the true / false value “Y” in the process of step S22, the content acquisition unit 21 sets the reproduction state flag F = the true / false value “Y” and the reproduction start time STS. = The current time NTS obtained from the system clock oscillator 24 is set, and settings for starting automatic reproduction are made (step S34).

  In this way, a track switching message is transmitted and received on the control line established by the transmission control units 22 and 23, and according to the message, the content piece of the destination track switched based on the time information is acquired and transmitted. The content receiving device 3a can perform smooth reproduction even when the track is switched.

  Note that communication between the transmission unit 23 and the reception unit 31 may be performed in accordance with RTP (Real-time Transfer Protocol, RFC1889) rules.

≪Application 1≫
As an application example 1 of the above embodiment, FIG. 5 shows a functional block diagram of a content distribution system 1b including a content distribution server 2 and a content receiving device 3b (karaoke device). The content distribution system 1b shown in FIG. 5 is a so-called communication karaoke system.

  The content distribution server 2 includes a content acquisition unit 21, a transmission control unit 22, a transmission unit 23, a system clock oscillation unit 24, and a content storage unit 25.

  The content receiving device 3b includes a receiving unit 31, a transmission control unit 32, a buffer unit 33, a system clock oscillation unit 34, a content reading unit 35, a reproduction unit 36b, an input unit 37, and a microphone input unit 38. In addition, about the same thing as said embodiment, the same number is attached | subjected and the detailed description is abbreviate | omitted.

  The playback unit 36b performs decoding according to the input content fragment, combines it with the audio signal from the microphone input unit, and then outputs the audio signal and video signal to a predetermined output device such as a speaker. Have For example, when the content segment is digital audio data encoded with high efficiency similar to MPEG, the playback unit 36 includes a high efficiency code decoder (decoder), a D / A converter, an analog amplifier, and the like. Is done.

  Here, the minimum requirement for composition is to reproduce two inputs from the content reading unit 35 and the microphone input unit 38 almost simultaneously. If the content segment type is audio, appropriate mixing synthesis and volume adjustment may be performed so as not to be unnatural with the audio from the microphone input unit 38.

  The microphone input unit 38 has a function of receiving an input of an audio signal captured by an audio capturing device such as a microphone and converting the audio signal into a data format handled by the playback unit 36b.

  In the communication karaoke system of FIG. 5, it is assumed that a certain content is transmitted from the content distribution server 2 to the content receiving device 3b.

  The content is, for example, a duet song of male vocals and female vocals. Track 1 contains only accompaniment data, track 2 contains accompaniment and male vocal data, and track 3 contains accompaniment and female vocal data. Assume that each is recorded.

  Then, by providing an appropriate track according to the user's request, it is possible to sing a duet song alone with a male vocal or a female vocal, and various services can be provided.

≪Application 2≫
As an application example 2 of the above embodiment, FIG. 6 shows a functional block diagram of a content distribution system 1c (communication karaoke system) including a content distribution server 2, a content receiving device 3b (karaoke device), and an authoring device 5. . The authoring device 5 may be housed in the same housing as the content distribution server 2 or may be housed in a separate housing. For convenience, the user who uses the authoring device 5 is called an editor.

  The content distribution server 2 includes a content acquisition unit 21, a transmission control unit 22, a transmission unit 23, a system clock oscillation unit 24, and a content storage unit 25.

  The content receiving device 3b includes a receiving unit 31, a transmission control unit 32, a buffer unit 33, a system clock oscillation unit 34, a content reading unit 35, a reproduction unit 36b, an input unit 37, and a microphone input unit 38. In addition, about the same thing as said embodiment, the same number is attached | subjected and the detailed description is abbreviate | omitted.

  Further, the authoring device 5 includes an authoring unit 51, a pitch conversion unit 52, a content transmission unit 53, an input unit 54, a microphone input unit 55, and a content primary storage unit 56.

  The authoring unit 51 uses the instruction input from the input unit 54 and the audio data from the microphone input unit 55 to create and edit content data such as new content data creation, track addition, content data deletion, and the like. It has a function of recording edited content data in the content primary storage unit 56.

  The pitch conversion unit 52 performs a pitch conversion for at least a semitone or a full tone on the original sound data (hereinafter referred to as source sound data) constituting the content (for example, a pitch described in JP-A-9-185392). A frequency shift algorithm using frequency domain conversion of speech, such as a conversion device).

  In this application example 2, the key variable k is an integer variable such that the scale of the reference source audio data is “0”, “+1” when shifted up by a semitone, and “−1” when shifted down by a semitone. Call. When the pitch conversion in a general karaoke apparatus is realized, the key variable k can take a range of at least −6 to 0 to +6.

  For example, when k = + 1, this corresponds to a minor second transposition, and when the original music is in C major, the key after the transposition is in D major. When k = -6, it corresponds to a decrease of 5 degrees. When the original music is in C major, the key after transposition is in F major.

  The reason why k = less than -6 (or greater than +6) is not used is that, for example, a semitone shift down by -6 means a transposition of +6 (4 degrees increase) after a semitone shift and then lowered by one octave. It is because it corresponds to. In the case of karaoke, as long as it matches the key intended by the user, it can be sung comfortably even if the performance octave is different.

  When the content file movement instruction and the destination distribution server name are input from the input unit 54, the content transmission unit 53 stores the content data stored in the content primary storage unit 56 in the distribution server indicated by the destination distribution server name. The content storage unit 25 has a function of transmitting via the network.

  The content transmission unit 53 has a function of recording content data on a recording medium such as a CD-R or a DVD-R. When content data is not transmitted via a network, the content data is provided on a recording medium.

  The input unit 54 has a function for the editor to accept each instruction input of a content data new creation instruction, a track addition instruction, a content data movement instruction, and a content data deletion instruction. For example, using a bitmap display and a keyboard, GUI parts such as a play button, a stop button, and a content selection dialog are provided to the user, and a track number is input using a numeric keypad and several stages of slide switches. Provide an operation switch that accepts.

  The microphone input unit 55 has a function of receiving input of an audio signal captured by an audio capturing device such as a microphone and converting the audio signal into a data format handled by the playback unit 36b to generate source audio data. The microphone input unit 55 may include an interface for receiving source audio data from the outside such as a CD-ROM drive or a network. Further, the microphone input unit 55 may include a microphone and a memory, and may record an audio signal for a predetermined time and convert it into source audio data. When the editor inputs a track addition instruction, source audio data is simultaneously taken into the authoring device 5 through the microphone input unit 55.

  The content primary storage unit 56 has a function of temporarily storing content data created and edited by the authoring unit 51.

  Next, the operation of the authoring device 5 will be described.

(1) New Creation of Content Data When the content data new creation instruction and the content file name CF1 are input from the input unit 54, the authoring unit 51 stores content data that does not include any track in the content primary storage unit 56. Create with content file name CF1.

(2) Deleting Content Data When the content data deletion instruction and the content file name CF1 are input from the input unit 54, the authoring unit 51 deletes the content data of the content file name CF1 recorded in the content primary storage unit 56. delete.

(3) Add track When the track adding instruction, content file name CF1, track number TN1, and key variable k are input from the input unit 54 and the source audio data is input from the microphone input unit 55, the authoring unit 51 It is determined whether or not the key variable k is “0”. If the key variable k is not “0”, the pitch conversion unit 52 is used to perform pitch conversion on the source audio data.

  Next, the authoring unit 51 opens the content data indicated by the content file name CF1, adds 1 to the total number of tracks, adds the track data indicated by the track number TN1, and sets the source audio data for each appropriate number of samples. The data is divided into segments, and if necessary, highly efficient coding is performed, and a frame number and time information are assigned and multiplexed. The track timestamp frequency is written by measuring the sampling frequency of the audio data.

  A plurality of tracks having different pitches are created in this way, and the authoring device 5 supplies the created content data to the content distribution server 2, thereby mounting the conventional pitch conversion unit 52 on the content receiving device 3 b side. This is unnecessary, and high-quality pitch conversion is possible when authoring content, so that the service quality can be improved.

  Further, even if it is not necessary to install the conventional pitch conversion unit 52 on the content receiving device 3b side, a service equivalent to that equipped with the pitch conversion unit 52 is possible, and the service cost can be drastically reduced. .

  In addition, since the pitch conversion unit 52 exists independently of the content receiving device 3b, the service quality is improved in the same manner in all the content receiving devices 3b regardless of the hardware production time and shipping time of the content receiving device. An effect is obtained.

  Also, when authoring content, some pitch ranges are converted by a mechanical process, and some pitches are actually played and sung using transposed music scores. By using the voice data, it is possible to realize a high-quality service that is impossible with the conventional method.

  In addition, for content that the content author does not consent to music processing such as pitch conversion, it is easy without adding special information to all the content receiving devices 3b, without adding a track whose pitch has been changed during authoring. It is also possible to prohibit pitch conversion reproduction for specific content.

  In the content distribution system 1c shown in FIG. 6, the content distribution server 2, the content receiving device 3b, and the authoring device 5 are only one each. However, as shown in FIG. The content distribution servers 2 may be connected, and the content receiving device 3b may be connected to each content distribution server 2.

  This is suitable as an example of a communication karaoke system that can provide services to a large number of users. The authoring device 5 performs a pitch conversion process and prepares content data in which content data having different pitches are recorded on a plurality of tracks, so that each content can be received only by copying the same content data to the plurality of content distribution servers 2. Even if the device 3b is not equipped with means for performing pitch conversion, it is possible to perform dynamic pitch conversion during playback by changing the track. In addition, even if the number of users increases and the number of sets of content distribution servers 2 and content receiving devices 3b increases, the time / calculation cost required for the pitch conversion process is always constant, enabling dramatic cost reductions. It becomes.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to these. In addition, all or part of the configuration requirements of the content distribution server 2, the content receiving device 3, and the authoring device 5 are realized as a computer-executable program, and are recorded in a computer-readable recording medium and provided in advance. It is also possible to do.

  A plurality of programs corresponding to the content distribution server 2 may be executed by a single physical computer. Further, a plurality of programs corresponding to the content receiving device 3 may be executed by a single physical computer.

  Further, a program corresponding to the content distribution server 2 and a program corresponding to the content receiving device 3 may be executed by a single computer. Furthermore, the program corresponding to the content distribution server 2 and the program corresponding to the authoring device 5 may be executed by a single physical computer.

It is a functional block diagram of the content delivery server 2 and the content receiver 3a in the content delivery system 1a (asynchronous model). It is a figure which shows the data structure of the content data which has several tracks. It is a sequence diagram which shows operation | movement of the transmission control part 22 of the content delivery server 2 at the time of transmission / reception of transmission control information, and the transmission control part 32 of the content receiver 3a. It is a flowchart which shows the reproduction time management process (transmission side) of the content acquisition part 21 at the time of reading content data. It is a functional block diagram of the content delivery system 1b (communication karaoke system) which consists of the content delivery server 2 and the content receiver 3b (karaoke apparatus). It is a functional block diagram of the content distribution system 1c (communication karaoke system) which consists of the content distribution server 2, the content receiver 3b (karaoke apparatus), and the authoring apparatus 5. It is a figure which shows the structural example which connected the several content delivery server 2 to the authoring apparatus 5. FIG. It is a functional block diagram of the content delivery server 102a and the content receiver 103a in an asynchronous model. It is a figure which shows an example of the data structure of content data. It is a flowchart which shows the reproduction time management process (transmission side) of the content acquisition part 1021 at the time of reading a content file. It is a flowchart which shows the reproduction time management process (reception side) of the content reading part 1034 using a network time stamp. It is a functional block diagram of the content delivery server 102b and the content receiver 103b which comprise the content delivery system 101b provided with a transmission control mechanism. It is a sequence diagram which shows operation | movement of the transmission control part 1025 and the transmission control part 1036 at the time of transmission / reception of transmission control information. It is a figure which shows the permutation of the content piece accumulate | stored in the buffer part 1032. It is a functional block diagram of the content distribution server 102c and the content receiver 103c which comprise the content distribution system 101c which can receive 2 tracks simultaneously. It is a flowchart which shows operation | movement of the content receiver 103c which has a multi-track simultaneous reception structure.

Explanation of symbols

1a, b Content distribution system 2 Content distribution server 3a, b Content reception device 4 IP network 5 Authoring device 21 Content acquisition unit 22 Transmission control unit 23 Transmission unit 24 System clock oscillation unit 25 Content storage unit 31 Reception unit 32 Transmission control unit 33 Buffer unit 34 System clock oscillation unit 35 Content reading unit 36 Playback unit 37 Input unit 38 Microphone input unit 51 Authoring unit 52 Pitch conversion unit 53 Content transmission unit 54 Input unit 55 Microphone input unit 56 Content primary storage unit 101a, b, c Content Distribution system 102a, b, c Content distribution server 103a, b, c Content receiving device 104 Network 1021 Content acquisition unit (A, B)
1022 Transmitter (A, B)
1023 System clock oscillation unit 1024 Content storage unit 1025 Transmission control unit 1031 Reception unit (A, B)
1032 Buffer part (A, B)
1033 System clock oscillation unit 1034 Content reading unit (A, B)
1035 Playback unit 1036 Transmission control unit 1037 Input unit 1038 Switching unit

Claims (3)

A content distribution server storing content data having a plurality of content segment data, and a content reproduction request to the content distribution server via the network, and the content distribution server responds to the reproduction request to the network. A content distribution method in a content distribution system comprising a content receiving device that receives and reproduces content fragment data transmitted via
The content data stored in the content distribution server is content data having a file name and a plurality of tracks, and the track data of each track has a track number and a plurality of data frames, and each data frame Is a frame number, time information indicating the timing of reproduction, and content fragment data, and the data frame of each track in the same frame number has the same time information,
The file name of the content data requesting reproduction from the content receiving device to the content distribution server is transmitted, and at least the preset track number transmitted from the content distribution server in response thereto, and the file The content receiving device receives the playback time information indicating the playback time length of the track having the preset track number in the content data of the name, and the content receiving device designates the desired track number and distributes the content A session establishing step of establishing a session between the content receiving device and the content distribution server by transmitting to a server;
When making a content playback start request after establishing the session,
In the content receiving device, a content playback start request message including the file name of the content data requesting the playback and playback range information indicating a playback time range is transmitted from the content receiving device to the content distribution server. And a process of
When the content distribution server receives the reproduction start request message, it specifies the frame number of the data frame including the content fragment data to be transmitted according to the reproduction range information in the reproduction start request message. The content fragment data requested to be reproduced, which is designated by the specified frame number, the file name in the reproduction start request message, and the track number designated by the content receiving device when the session is established. Obtaining from the stored content data and transmitting to the content receiving device;
When making a request to switch the playback target track after establishing the session,
In the content receiving device, a step of transmitting a switching request message including a switching destination track number for switching playback tracks from the content receiving device to the content distribution server;
In the content distribution server, when the switching request message is received after receiving the reproduction start request message, the reproduction order is the last among the content piece data already sent at the time of receiving the switching request message. Based on the time information in the data frame including the content segment data, the data frame including the content segment data to be reproduced continuously with the content segment data whose reproduction order is last. The content number data specified by the specified frame number and the switching destination track number in the switching request message is acquired from the stored content data, Transmitting to the content receiving device;
A content distribution method characterized by comprising: In response to a playback request from the content receiving device, the content segment data requested to be played back is selected from content data having a plurality of content segment data, and the selected content segment data is transmitted to the content receiving device via the network. A content distribution server,
Content data having a file name and a plurality of tracks. The track data of each track has a track number and a plurality of data frames, and each data frame has a frame number and time information indicating a reproduction timing. , And a content storage means for storing content data in which the data frames of the tracks in the same frame number have the same time information.
The file name of the content data requested to be reproduced is received from the content receiving device, and at least the track number set in advance according to the file name, and the preset track number in the content data of the file name Session with the content receiving device by transmitting playback time information indicating the playback time length of the track to the content receiving device and then receiving the desired track number designated by the content receiving device. Establish
After the session is established, when a content playback start request is made at the content receiving device, the file name of the content data requested to be played from the content receiving device, and playback range information indicating the time range to play back Receiving a playback start request message for content containing
Transmission for receiving a switching request message including a switching destination track number for switching the playback track from the content receiving device when a request for switching the playback target track is made in the content receiving device after the session is established Control means;
When the transmission control means receives the reproduction start request message, the frame number of the data frame including the content fragment data to be transmitted is specified according to the reproduction range information in the reproduction start request message, The content fragment of the content requested to be played, which is specified by the identified frame number, the file name in the playback start request message, and the track number specified by the content receiving device when the session is established Obtaining data from the content storage means;
When the transmission control unit receives the switching request message after receiving the reproduction start request message, the reproduction order is the last of the content piece data already sent at the time of receiving the switching request message. Based on the time information in the data frame including the content segment data, the data frame including the content segment data to be reproduced continuously with the content segment data whose reproduction order is last. Content acquisition means for specifying the frame number and acquiring the content fragment data specified by the specified frame number and the switching destination track number in the switching request message from the content storage means;
Transmitting means for transmitting the content fragment data acquired by the content acquisition means to the content receiving device;
A content distribution server comprising: A content reproduction server that stores content data having a plurality of pieces of content data is requested to reproduce the content via the network, and is transmitted from the content distribution server via the network in response to the reproduction request. A content receiving device for receiving and playing back content fragment data,
The content data stored in the content distribution server is content data having a file name and a plurality of tracks, and the track data of each track has a track number and a plurality of data frames. The frame has a frame number, time information indicating reproduction timing, and content fragment data, and the data frame of each track in the same frame number has the same time information,
The file name of the content data requesting reproduction is transmitted, and the previously set track number transmitted from the content distribution server in response to the file name and the content data of the file name are set in advance. A session with the content distribution server is established by receiving reproduction time information indicating the reproduction time length of the track having the track number, and then specifying the desired track number and transmitting it to the content distribution server And
When the content reproduction start request is made after the session is established, the content distribution start request message including the file name of the content data to be reproduced and the reproduction range information indicating the reproduction time range is transmitted to the content. To the server,
A transmission control means for transmitting a switching request message including a switching destination track number for switching the reproduction track to the content distribution server when performing a switching request of the reproduction target track after the establishment of the session ;
In the content distribution server, when the switching request message is received after receiving the reproduction start request message, the reproduction order is the last among the content piece data already sent at the time of receiving the switching request message. Based on the time information in the data frame including the content segment data, the data frame including the content segment data to be reproduced continuously with the content segment data whose reproduction order is last. Receiving means for receiving, from the content distribution server, the content segment data specified and transmitted by the specified frame number and the switching destination track number in the switching request message And
A content receiving apparatus comprising:

Images