JP3893643B2 - Signal multiplexing method and transmission signal generating apparatus using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a signal multiplexing method and a transmission signal generation apparatus using the same. Specifically, when video signals, audio signals, and the like of a program of a plurality of channels are encoded and then multiplexed and transmitted, time management information for performing time control in decoding processing of the transmitted signal is encoded for each program. Time reference information for setting the synchronization information, which is a reference for time in the decoding process, to a desired value is added to the signal obtained by multiplexing the encoded signal of each program. And the time reference information are generated based on the same reference time, thereby preventing the reference time from being shifted on the receiving side with a simple configuration.
[0002]
[Prior art]
In digital television broadcasting such as DVB (Digital Video Broadcasting), MPEG2 (Moving Picture Coding Experts Group Phase 2) is adopted as a data compression method. In this digital television broadcast, broadcasting is distributed to each home using various transmission paths such as satellite waves and cables. However, data compression can be used to transmit programs of multiple channels on one transmission path. Channelization is planned. For example, a plurality of transponders are mounted on one broadcasting satellite, and if one transponder has a bandwidth of 36 Mbps and a bandwidth per program is 4 Mbps, nine programs can be broadcast simultaneously per transponder.
[0003]
In the MPEG2 system, a method for multiplexing and storing and transmitting a plurality of video / audio / data is standardized (Recommendation H.222.0). In this standard, a transmission path (for example, broadcasting or communication) in which an error occurs is standardized. A transport stream TS that is assumed to be used in a program stream PS and a program stream PS that is assumed to be used in a transmission path (for example, a CD-ROM) without errors. Note that the transport stream TS is composed of short packets having a fixed length of 188 bytes. Since the packet length is short, it is easy to deal with errors.
[0004]
Here, the digital television broadcasting system will be described with reference to the system diagram of FIG. In the MPEG encoder 10 to which the video signal or audio signal of one program is supplied, the video signal Dv1, audio signal Da1, and data such as time information are encoded and packetized, multiplexed and transport stream TS1. Is generated. The transport stream TS1 is supplied to the multiplexer 40. Similarly, the MPEG encoders 20 and 30 to which the video signals Dv2 and Dv2 and audio signals Da3 and Da3 of other programs are supplied generate transport streams TS2 and TS3 and supply them to the multiplexer 40.
[0005]
The multiplexer 40 is supplied with service information and management information of digital television broadcasting such as “program information” and “limited reception information” as transport streams TS4 and TS5, and these transport streams TS1 to TS5 are supplied. A multiplexed multi-channel transport stream TSm is generated and transmitted as a transmission signal.
[0006]
On the receiving side, the demultiplexer 60 separates the transport stream TSc of the desired channel from the multi-channel transport stream TSm, and supplies it to the MPEG decoder 70. In the MPEG decoder 70, the video signal packet and the audio signal packet are separated from the transport stream TSc of the desired channel. Further, the separated packet signal can be decoded to obtain a video signal Dvc and an audio signal Dac of a desired channel.
[0007]
[Problems to be solved by the invention]
By the way, in the multiplexer 40, transport streams are supplied from a plurality of MPEG encoders, and when the input phases of the plurality of transport streams do not coincide with each other in time, the transport streams are output as they are. When the input phases coincide with each other in time, multiplexing is performed with the output timing of one of the coincident transport streams being delayed.
[0008]
However, if the delayed transport stream includes PCR (Program Clock Reference) which is time reference information for reproducing the reference time by the MPEG decoder, the PCR is caused by the arrival of the PCR. Since the reference time in the MPEG decoder is set on the basis of the data and the like, the set time is set and the reference time is shifted.
[0009]
For this reason, in the conventional transmission signal generator, PCR data management is performed as shown in FIG. In FIG. 7, parts corresponding to those in FIG.
[0010]
A video signal Dv1 and an audio signal Da1 are supplied to the MPEG encoder 10 in FIG. 7, and the video signal Dv1 is encoded by the video encoder unit 11 into a video stream. Also, the audio signal Da1 is encoded by the audio encoder unit 12 to be an audio stream.
[0011]
An STC (System Time Clock) unit 13 is a clock that generates a time reference for the MPEG encoder 10. Based on the time of the STC unit 13, the video encoder unit 11 and the audio encoder unit 12 generate reproduction outputs used in the MPEG decoder. A PTS (Presentation Time Stamp) that is time management information and a DTS (Decoding Time Stamp) that is decoding time management information are generated. Further, the video encoder unit 11 generates a PES (Packetized Elementary Stream) packet from the information such as the PTS and DTS and the video stream and supplies the PES (Packetized Elementary Stream) packet to the multiplexing circuit 14. In the audio encoder unit 12, a PES packet is generated from the PTS information and the audio stream and supplied to the multiplexing circuit 14.
[0012]
In the multiplexing circuit 14, the PES packets supplied from the video encoder unit 11 and the audio encoder unit 12 are multiplexed. Further, a PCR is generated based on the time of the STC unit 13, and a transport stream TS1 is generated based on the PCR and the multiplexed PES packet.
[0013]
Similarly, the MPEG encoders 20 and 30 generate a transport stream TS2 and a transport stream TS3. Note that the STC units 13, 23, and 33 of the MPEG encoders 10, 20, and 30 generate times independently of each other.
[0014]
The transport streams TS1, TS2, and TS3 are supplied to the input units 41, 42, and 43 of the multiplexer 40, respectively. The multiplexer 40 has an STC unit 46, and the time of the STC unit 46 is supplied to the input units 41, 42, and 43.
[0015]
The input units 41, 42, and 43 are configured using a FIFO (First-In First-Out) memory, and the transport streams TS1, TS2, and TS3 arrive together with the supplied transport streams TS1, TS2, and TS3. The time is stored.
[0016]
The multiplexing circuit 44 multiplexes the transport streams TS1, TS2, and TS3 stored in the input units 41, 42, and 43. Here, when there is a temporally matching transport stream TS, one of them is delayed and then multiplexed and supplied to the PCR correction circuit 45.
[0017]
In the PCR correction circuit 45, when the multiplexed transport stream TS includes a PCR, a time difference between the arrival time of the transport stream TS and the current time of the STC unit 46 is detected. By adding the detected time difference to the PCR, the PCR is corrected and a multi-channel transport stream TSm, which is a transmission signal, is generated.
[0018]
For this reason, in the MPEG decoder, the PCR is corrected even when the transport streams coincide with each other in time and one of them is delayed. Therefore, the reference time in the MPEG decoder set based on this PCR is set. The occurrence of a time lag is prevented.
[0019]
As described above, in the conventional transmission signal generation apparatus that generates a transmission signal of a plurality of channels, even if the transport streams coincide with each other in time and one of them is delayed, a reference time shift occurs in the MPEG decoder. In order to prevent this from happening, the arrival time of the transport stream is stored, the time difference between the arrival time and the current time is detected, and the PCR is corrected using the detected time difference. A circuit was needed.
[0020]
Accordingly, the present invention provides a signal multiplexing method and a transmission signal generation device that can easily generate a transmission signal of a plurality of channels with a simple circuit configuration so as not to cause a reference time shift on the receiving side.
[0021]
[Means for Solving the Problems]
A signal multiplexing method according to the present invention is a method of multiplexing an input signal as an encoded signal, the time management information used for performing time control in the decoding process of the encoded signal, and the time A step of generating a reference time as a reference of time reference information for setting reference synchronization information to a desired value, a step of supplying the generated reference time to the signal multiplexing means and the plurality of encoders; A step of encoding an input signal at each of the encoders based on the received reference time and outputting an encoded signal; and a signal multiplexing of the encoded signal output from each of the encoders based on the reference time And a step of multiplexing by means.
[0022]
The signal multiplexing apparatus according to the present invention includes a plurality of encoders that encode an input signal based on a reference time and output an encoded signal, and each encoded signal output from the encoder is based on the reference time. Signal multiplexing means for multiplexing and outputting, and each of the encoders and reference time generating means for supplying a reference time to the signal multiplexing means, each of the encoders in the decoding process of the encoded signal, Time management information generating means for generating time management information used for performing time control based on the reference time, and the signal multiplexing means is a decoding process of the multiplexed encoded signal, Time reference information generating means for generating time reference information for setting reference synchronization information to a desired value based on the reference time, and the reference time generating means Management information and generates a reference time as a reference of the time reference information is characterized in that the supply to each, and the time reference information generating means of the time management information generating means.
[0023]
In the present invention, video signals, audio signals, etc. of a program of a plurality of channels are encoded by the MPEG encoder, and time control or reproduction of reproduction output is performed in the decoding process of the encoded signal by the time management information generating means. Time management information for controlling the order is generated and added. The encoded signal of each program to which this time management information is added is multiplexed by signal multiplexing means. Time reference information for reproducing the reference time in the decoding process generated by the time reference information generating means is added to the multiplexed signal, and for example, an MPEG2 multi-channel transport stream is obtained. Since the time management information and the time reference information are generated based on the time generated by the reference time generating means, the time reference information and the time management information of each program are synchronized with each other.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Subsequently, an embodiment of a transmission signal generating apparatus according to the present invention will be described in detail with reference to the drawings.
[0025]
FIG. 1 is a system diagram showing an embodiment of a transmission signal generating apparatus according to the present invention, and shows a case where, for example, three programs are multiplexed and output. In FIG. 1, parts corresponding to those in FIG.
[0026]
In the station time code generating unit 50, which is the reference time generating means shown in FIG. 1, a time serving as a reference for the entire transmission signal generating device is generated and supplied to the MPEG encoders 10a, 20a, 30a and the multiplexer 40a.
[0027]
A video signal Dv1 and an audio signal Da1 are supplied to the MPEG encoder 10a, and the video signal Dv1 is encoded by the video encoder unit 11 to be a video stream. Also, the audio signal Da1 is encoded by the audio encoder unit 12 to be an audio stream.
[0028]
The STC unit 13 is supplied with a reference time from the station time code generation unit 50, and the time reference of the MPEG encoder 10 is generated based on this time. Based on the time generated by the STC unit 13, the video encoder unit 11 and the audio encoder unit 12 generate PTS that is playback management time management information and DTS that is decoding time management information used in an MPEG decoder described later. The Further, the video encoder unit 11 generates a PES packet from information such as PTS and DTS and a video stream. The audio encoder unit 12 generates a PES packet from information such as PTS and DTS and an audio stream.
[0029]
Here, FIG. 2 shows the structure of the PES packet. The video stream shown in FIG. 2A or the audio stream shown in FIG. 2B is divided into an appropriate length, and the PES packet shown in FIG. 2C is generated. This PES packet is configured as shown in FIG. 2D.
[0030]
In FIG. 2D, the packet start code is composed of a start code which is a 24-bit fixed value and an 8-bit stream ID, and a stream packetized by this stream ID is defined. The next 16 bits indicate the data length of the packet. “10” is an identification code indicating the MPEG2 program stream PS. Flags are placed together in the next 14 bits, and option data is placed in the conditional coding corresponding to these flags. The header length of the PES packet is indicated by 8 bits following the flags. In the conditional coding section, PTS and DTS are indicated by (33 + 7) bits. The stuffing byte is dummy data for making the data length constant even when there is no PTS or DTS. Following the conditional coding, packet data of a data stream of information relating to a video stream, an audio stream or a program is placed.
[0031]
The PES packet configured in this way is supplied to the multiplexing circuit 14 and multiplexed. Further, the multiplexing circuit 14 divides the multiplexed PES packet to generate a transport stream TS1.
[0032]
Here, the structure of the transport stream TS is shown in FIG. As shown in FIG. 3A, the transport stream TS is composed of transport packets having a fixed length of 188 bytes, and this transport packet has the structure shown in FIG. 3B.
[0033]
In FIG. 3B, the 8-bit synchronization signal is data for detecting the head of the transport packet by the MPEG decoder. The error display indicates whether or not there is a bit error in this packet. The unit start display indicates that a new PES packet starts from a payload described later of this packet. The transport packet priority indicates the importance of this packet. 13-bit PID (Packet Identification) is stream identification information. In the scramble control, the presence / absence / type of payload scramble is indicated. In the adaptation field control, the presence / absence of an adaptation field and a payload described later are indicated. In the 4-bit cyclic counter, whether or not a part of packets having the same PID is partially discarded is determined based on the continuity of the count information. The adaptation field is configured as shown in FIG. 3C, and the data of the divided PES packet is placed in the payload following the adaptation field.
[0034]
In FIG. 3C, the adaptation field length is indicated by the first 8 bits of the adaptation field. In the discontinuous display, it is indicated that the system clock is reset and becomes new contents in the next packet having the same PID. The random access display indicates the start of a video sequence header or audio frame, and the entry point at the time of random access can be detected by this random access display. The stream priority indication indicates that an important part of the individual stream is in the payload of this packet. A flag is provided after the stream priority display, and an optional field of conditional coding is set by this flag. After this optional field, a stuffing byte that is invalid data is provided as necessary.
[0035]
Optional fields include PCR as time reference information, OPCR (Original Program Clock Reference) as original program reference time, splice countdown indicating the number of transport packets of the same PID up to the editable point, and the like. ing.
[0036]
In the MPEG encoders 20a and 30a, as in the MPEG encoder 10a, the time reference is generated by the STC units 23 and 33 based on the time from the station time code generation unit 50, and the video encoder unit using the time reference PES packets are generated by the audio encoder units 22 and 32 and supplied to the multiplexing circuits 24 and 34. The multiplexing circuits 24 and 34 also generate transport streams TS2 and TS3 in the same manner as the multiplexing circuit 14.
[0037]
Thus, the transport streams TS1, TS2, TS3 generated by the MPEG encoders 10a, 20a, 30a are supplied to the input sections 41a, 42a, 43a of the multiplexer 40a, respectively.
[0038]
The input units 41, 42, and 43 are configured using a FIFO (First-In First-Out) memory, and transport streams TS 1, TS 2, TS 3 are sequentially stored and read out and supplied to the multiplexing circuit 44. Is done.
[0039]
The multiplexing circuit 44 multiplexes the transport streams TS1, TS2, and TS3 stored in the input units 41, 42, and 43. Here, when there is a temporally matching transport stream TS, one of them is delayed and multiplexed and supplied to the PCR adding unit 47.
[0040]
The PCR adding unit 47 is supplied with the time generated by the STC unit 48 based on the reference time of the station time code generating unit 50, and the PCR is added to the multiplexed transport stream so that a multi-channel transcoder is added. A port stream TSm is transmitted.
[0041]
On the receiving side, the transport stream TSc of the desired program is separated from the multi-channel transport stream TSm by the demultiplexer and supplied to the MPEG decoder. Here, the structure of the MPEG decoder is shown in FIG.
[0042]
In FIG. 4, the transport stream TSc is supplied to the separation unit 71 of the MPEG decoder 70 and separated into PES packets of video signals and audio signals.
[0043]
The PES packet of the video signal is supplied to the video decoder unit 73 via the buffer 72. The PES packet of the audio signal is supplied to the audio decoder unit 75 via the buffer 74. In addition, the PCR of the transport stream TSc is supplied to the STC unit 76.
[0044]
FIG. 5 is a diagram showing a configuration of the STC unit 76, and the STC unit 76 is configured by a PLL (Phase Locked Loop). The PCR of the transport stream TSc is supplied to the adder 761 and the counter 762. In the counter 762, the counter 762 is set by PCR based on the signal LD indicating the PCR supply timing of the transport stream TSc and a system clock signal CK from a voltage controlled oscillator (VCO) 765 described later. The PCR set from 762 is output and supplied to the adder 761.
[0045]
In the adder 761, the PCR of the transport stream TSc supplied from the separation device and the PCR-inverted data of the PCR supplied from the counter 762 are added, and the PCR of the transport stream TSc supplied from the separation device is added. And the error data of the PCR supplied from the counter 762 is supplied to the D / A converter 763. The error data supplied to the D / A converter 763 is converted into an analog signal and supplied to the voltage controlled oscillator 765 via the low pass filter 764. For this reason, the frequency of the system clock signal CK output from the voltage controlled oscillator 765 is assumed to coincide with the frequency (27 MHz) of the system clock signal on the transmission side, ensuring the accuracy of the PCR timing and ensuring the correct reference time. It is reproduced. The reference time output from the counter 762 is supplied to the video decoder unit 73 and the audio decoder unit 75.
[0046]
The video decoder unit 73 and the audio decoder unit 74 decode the PES packet signal based on the reference time from the STC unit 76 and the PTS and DTS of the PES packet to generate the video signal Dvc and the audio signal Dac.
[0047]
As described above, according to the above-described embodiment, the STC unit 13a of the MPEG encoder 10a and the STC unit 23a of the MPEG encoder 20a are based on the overall reference time generated by the station time code generation unit 50 on the transmission side. Since the STC unit 33a of the MPEG encoder 30a and the STC unit 48 of the multiplexer 40a generate the reference time, the PTS and DTS of each channel are generated in synchronism and the PCR is also generated in synchronism with the transmission signal. A multi-channel transport stream TSm is generated.
[0048]
On the receiving side, a system clock signal is generated in synchronization with the PCR of the transport stream TSc selected from the multi-channel transport stream TSm, and a signal decoding process is performed based on the PTS and DTS synchronized with the PCR. Thus, the signal can be reproduced satisfactorily without causing a reference time shift.
[0049]
Furthermore, since the transmission side stores the arrival time of the TS packet and it is not necessary to correct the PCR from the actually multiplexed time, the configuration can be made simple and small.
[0050]
【The invention's effect】
According to this invention, time management information for controlling reproduction output time control and reproduction order when decoding the encoded signal is added to each of the encoded signals obtained by a plurality of encoders. And multiplexed by the signal multiplexing means. Time reference information for reproducing the reference time in the decoding process generated by the time reference information generating means is added to the multiplexed signal to generate a transmission signal. The time management information and the time reference information are generated and synchronized based on the time generated by the reference time generating means.
[0051]
This eliminates the need for a complicated circuit for correcting the time reference information required when multiplexing the time reference information added to the encoded signal from each encoder. A transmission signal of a plurality of channels that does not cause a reference time shift can be easily generated.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a transmission signal generating apparatus according to the present invention.
FIG. 2 is a diagram illustrating a structure of a PES packet.
FIG. 3 is a diagram illustrating a configuration of a transport stream.
4 is a diagram showing a configuration of an MPEG decoder 70. FIG.
5 is a diagram showing a configuration of an STC unit 76. FIG.
FIG. 6 is a system diagram of a digital television broadcasting system.
FIG. 7 is a diagram illustrating a configuration of a conventional transmission signal generation device.
[Explanation of symbols]
10, 10a, 20, 20a, 30, 30a ... MPEG encoder, 11, 21, 31 ... video encoder, 12, 22, 32 ... audio encoder, 13, 13a, 23, 23a, 33, 33a , 46, 48, 76 ... STC section, 14, 24, 34, 44 ... multiplexing circuit, 40, 40a ... multiplexer, 41, 41a, 42, 42a, 43, 43a ... input section 45... PCR corrector 47. PCR adder 50. Station time code generator 60. Demultiplexer 70 MPEG decoder

Claims (5)

A method of multiplexing an input signal as an encoded signal,
In the decoding process of the encoded signal, a reference time serving as a reference of time reference information for setting time management information used for time control and synchronization information as a reference of time to a desired value is generated. Steps,
Supplying the generated reference time to a signal multiplexing means and a plurality of encoders;
Encoding an input signal at each of the encoders based on the supplied reference time and outputting an encoded signal; and
A signal multiplexing method comprising: multiplexing the encoded signals output from the encoders by the signal multiplexing means based on the reference time. The encoded signal is a signal obtained by separating and encoding an MPEG2 encoded stream,
The time management information is PTS (Presentation Time Stamp) or DTS (Decoding Time Stamp),
The signal multiplexing method according to claim 1, wherein the time base information is a PCR (program time base reference value). A plurality of encoders that each encode an input signal based on a reference time and output an encoded signal;
Signal multiplexing means for multiplexing and outputting each encoded signal output from the encoder based on a reference time;
A reference time generating means for supplying a reference time to each of the encoders and the signal multiplexing means,
Each of the above encoders
Time management information generating means for generating time management information used for performing time control in the decoding process of the encoded signal based on the reference time,
The signal multiplexing means is
Time reference information generating means for generating time reference information for setting synchronization information serving as a time reference to a desired value in the decoding process of the multiplexed encoded signal based on the reference time ,
The reference time generating means is
A transmission signal generating apparatus, characterized in that a reference time serving as a reference for the time management information and the time reference information is generated and supplied to each of the time management information generating means and the time reference information generating means. The encoder is
Video encoder means for encoding a video signal in the input signal;
Audio encoder means for encoding the audio signal in the input signal;
Sound and video multiplexing means for multiplexing the encoded audio signal and video signal,
The video encoder means comprises:
Input the time management information generated by the time management information generation means, encode the video signal based on the time management information, and output the encoded signal to the sound video multiplexing means,
The audio encoder means includes
4. The transmission signal generation according to claim 3, wherein the time management information is input, the audio signal is encoded based on the time management information, and the encoded signal is output to the audio / video multiplexing means. apparatus. The signal multiplexing means is
A plurality of input units for inputting the respective encoded signals;
A multiplexing unit that multiplexes signals output from the plurality of input units;
4. The transmission according to claim 3, further comprising: a time information adding unit that inputs the time reference information generated by the time reference information generating means and adds the time reference information to the multiplexed signal. Signal generator.

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