Lecture2-Multimedia Systems

Multimedia Systems
Dr. Wissam Alkhadour

WHAT IS MULTIMEDIA?
 A Multimedia System is a system capable of

processing multimedia data and applications.
 A Multimedia System is characterized by the
processing, storage, generation, manipulation and
rendition of Multimedia information.
Characteristics of a Multimedia
System
 A Multimedia system has four basic

characteristics:
 Multimedia systems must be computer controlled.
 Multimedia systems are integrated.
 The information they handle must be represented
digitally.
 The interface to the final presentation of media is
usually interactive.
Challenges for Multimedia
Systems
 Distributed Networks
 Temporal relationship between data
– Render different data at same time — continuously.
– Sequencing within the media
playing frames in correct order/time frame in video.
 Synchronization — inter-media scheduling E.g.
Video and Audio conversation.
Key Issues for Multimedia
Systems
 The key issues multimedia systems need to

deal with here are:
-How to represent and store temporal
information.
-How to strictly maintain the temporal
relationships on play
Key Issues for Multimedia
Systems
 back/retrieval
 What process are involved in the above.
 Data has to be represented digitally.
 Conversion, Sampling etc.
 Large Data Requirements — bandwidth,
storage, Data compression is usually
mandatory.
Desirable Features for a
Multimedia System
 Given the above challenges the following

feature a desirable (if not a prerequisite) for a
Multimedia System:
-Very High Processing Power — needed to
deal with large data
-processing and real time delivery of media.
Multimedia System
 Special Hardware/Software needed.

 Data Representations — File Formats that support
multimedia should be easy to handle yet allow for
compression/decompression in real-time.
 Efficient and High I/O —input and output to the file
subsystem needs to be efficient and fast. Needs to
allow for real-time recording as well as playback of
data
Multimedia System
 Special Operating System —to allow access

to file system and process data efficiently
and quickly.
 Storage and Memory — large storage units.
 Network Support — Client-server systems -
Software Tools — user friendly tools needed
to handle media, design and develop
applications to deliver media.
Components of a Multimedia
System
 Now let us consider the Components (Hardware and

Software) required for a multimedia system:
- Capture devices — Video Camera, Video Recorder,
Audio Microphone, Keyboards, mice, graphics
tablets.
 Storage Devices — Hard disks, CD-ROMs, DVD-
ROM, etc..
 Communication Networks — Local Networks,
Intranets, Internet, Multimedia or other special high
speed networks
Components of a Multimedia
System
 Computer Systems — Multimedia Desktop

machines, Workstations.
 Display Devices, quality speakers, HDTV.
monitors, Colour printers etc
A Brief Look at Multimedia Data:
Input and Format
Text and Static Data

 Source: keyboard, speech input, optical
character recognition,
 data stored on disk.
 Stored and input character by character:
Input and Format
Text and Static Data
 Storage of text is 1 byte per char / more bytes for

Unicode.
– For other forms of data (e.g. Spreadsheet files). May
store format as text (with formatting) others may use
binary encoding.
 Format: Raw text or formatted text e.g HTML, Rich
Text Format (RTF), Word or a program language
source (C, Pascal, etc..
Input and Format
Graphics
 Format: constructed by the composition of
primitive objects such as lines, polygons,
circles, curves and arcs.
 Input: Graphics are usually generated by a
graphics editor program (e.g. Illustrator).
Graphics are usually editable.
Input and Format
 Graphics
 Graphics input devices: keyboard (for text and cursor

control), mouse, trackball or graphics tablet.
 graphics standards : OpenGL, PHIGS, GKS
 Graphics files usually store the primitive assembly
 Do not take up a very high storage overhead.
Input and Format
Images
 Still pictures which (uncompressed) are represented
as a bitmap (a grid of pixels).
 Input: digitally scanned photographs/pictures or
direct from a digital camera.
 Input: May also be generated by programs “similar”
to graphics, or animation programs.
Input and Format
 Images
 Stored at 1 bit per pixel (Black and White), 8 Bits per
pixel (Grey Scale, Colour Map) or 24 Bits per pixel
(True Colour)
 Size: a 512x512 Grey scale image takes up 1/4 MB,
a 512x512
 24 bit image takes 3/4 MB with no compression.
Input and Format
Images
 This overhead soon increases with image
size — modern
 high digital camera 10+ Megapixels 29MB
uncompressed!
 Compression is commonly applied.
Input and Format
Audio
 Audio signals are continuous analog signals.
 Input: microphones and then digitised and
stored
 CD Quality Audio requires 16-bit sampling at
44.1 KHz
 Even higher audiophile rates (e.g. 24-bit, 96
KHz)
Input and Format
Audio
 1 Minute of Mono CD quality
(uncompressed) audio requires 5 MB.
 1 Minute of Stereo CD quality
(uncompressed) audio requires 10 MB.
 Usually compressed (E.g. MP3, AAC, Flac,
Ogg Vorbis).
Input and Format
Video
 Input: Analog Video is usually captured by a video
camera and then digitized.
 There are a variety of video (analog and digital)
formats
 Raw video can be regarded as being a series of
single images.
 There are typically 25, 30 or 50 frames per second.
Input and Format
Video
 E.g. A 512 512 size monochrome video images take
6.25MB for a second to store uncompressed.
 Typical PAL digital video (720 576 pixels per colour
frame).
 High Definition video on Blu-ray (up to 19201080 = 2
Megapixels per frame) Digital video clearly needs to
be compressed for most times.
Multimedia Data Compression
 How can we compress data?

 Lossy v Lossless :
 Lossless : Ideal (e.g. zip, unix compress) not good
enough for MM data!
 Lossy :Throw away nonessential (perceptually less
relevant) parts of the data stream FILTER the data
somehow. Examples: MP3, JPEG, MPEG Video

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Multimedia Systems

Dr. Wissam Alkhadour

 A Multimedia System is a system capable of

 A Multimedia system has four basic

 The key issues multimedia systems need to

 Given the above challenges the following

 Special Hardware/Software needed.

 Special Operating System —to allow access

 Now let us consider the Components (Hardware and

 Computer Systems — Multimedia Desktop

Text and Static Data

Text and Static Data

 Storage of text is 1 byte per char / more bytes for

 Graphics input devices: keyboard (for text and cursor

 How can we compress data?

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