Data Compression and Network Video by Mark Pelley Navin 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 Mbps 2.5 Mb MPEG kbps 700 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 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.