Data Compression and Network Video

by

Mark PelleyNavin Dodanwela

Digitizing Video

• Converting Analog video for storage on digital media:Sequence of Stills (standard 30 fps)

• Raw video at a resolution of 640 x 480 and 256 colors = 66 GB per hour

• High demands placed on hardware - need for compression is self-evident

AVI

• AVI (Audio Video Interleave) - common PC format developed by Microsoft.

• The format is interleaved such that video and audio data are stored consecutively (i.e., segment of video data is immediately followed by a segment of audio data)

• AVI files are limited to 320 x 240 resolution, and 30 frames per second

• Cheap, because it does not require special hardware

• Supports compression

MPEG-1

• Motion Picture Expert Group 1: Coding of moving pictures and associated audio for digital storage media at up to about 1.5 Mbit/s

• Uses DCT (Direct Cosine Transformation) to reduce storage requirements within a frame

• Uses Motion Compensation to exploit limited differences in two successive frames

• “Lossy” compression format

MPEG-1 (contd....)

MPEG-2• Generic coding of moving pictures and associated

audio of the TV-scanning pattern

• MPEG-1 originally intended for non-interlaced displays

• MPEG-2 permits encoding of interlaced video input

• Efficiency gain of only 20% over MPEG-1; however, broke new ground in terms of collaboration between companies and ensured a standard used up to the present day

ASF

• Advanced Streaming Format: Designed for “streaming” video over a network

• ASF is a set of rules describing how multimedia data is organized and laid out on a disk - optimized for streaming over a network

Comparison of Formats

AVI Raw - 64 Mb MPEG - 1.2 Mbps2.5 Mb

MPEG - 250 kbps700 kb

Advantages and Applications of Streaming Media

• Eliminates need to download to a local storage device

• Allows for video conferencing, training events• Used to broadcast trade shows, product launches

to larger audience• Enables delivery and sale of Pay-Per-Stream

content over the internet, TV / Video on-demand

Disadvantages and Constraints

• Transmission– TV quality MPEG requires minimum bandwidth of 1.5

- 2 Mbit/s

– Streaming Media requires (almost) constant transmission rate; causes net-congestion

– Transmission media and Network architecture selection depends on the number of users and the compression format used

– High speed network architecture such Ethernet 100BaseT or ATM advisable

• Cost– Microsoft Net Show Theater Server: Product developed

for real-time transmission of digitized video data within a private network.

– Using 100BaseT network card, 40 simultaneous streams at 2 Mbps possible per server used

– Support of 200 clients costs approximately $150,000 for hardware and software - not including cost of transmission media!!

Disadvantages and Constraints (contd....)

Summary

• Technology still on the bleeding edge

• Several commercial firms use streaming media on a small scale

• Future promising for streaming media– AOL purchase of Time-Warner indicates move towards

combination of high-speed networks and TV content.