Digital Video
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Digital Video |
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Several standard video compression algorithms (codecs), are being widely used on various platforms. The algorithms fall into one of two classifications: symmetric codec or asymmetric codec. The symmetric codecs require inverse operations to decompress the format. Asymmetric codecs use different compression|decompression methods. More processing time is spent in compressing to achieve low storage to allow for shorter decompression time.
Produced by the Apple corporation for both Macintosh and Windows it is actually a system for playing digital video. It allows the use of different codecs in addition to Apple's own proprietary format.
Microsoft launched Video For Windows as an alternative to Quicktime for Windows. Like Quicktime it is an open-architecture system, allowing the use of different codecs.
A codec based upon the Joint Photographics Expert Group (JPEG) graphic format, MJPEG performs only intraframe compression. Due to the lack of interframe compression it requires special video hardware to deliver acceptable speed and quality.
A platform independent symmetric codec proposed by the Motion Picture Experts Group. Two standards currently exist. MPEG-1 was designed for CD-ROM single-speed (150 KB/sec), playback in a 320 X 240 window at 30 fps. MPEG-2 was designed for studio-quality video in a 704 X 480 window at fps. For more details, look at the tutorial by Dane Dwyer and Michael Swafford, or the discussion at Terran Interactive.
Produced by SuperMac Technology, cinepak is an asymetric codec designed for 24-bit video in a 320 X 240 window for single-speed CD-ROM drives. Compression typically takes 300 times longer than decompression. You might want to see a comparison of Cinepak versus Indeo.
Intel produced the Indeo asymmetric codec for real time compression on special Intel hardware. Playback can take place on a Intel 486 processor without any hardware assistance. It produces high-quality talking-head video but is less efficient than Cinepak at motion sequences.
The Digital Video Interactive standard has been in existence longer than most other formats. It requires off-line supercomputer processing power for the compression. Intel provides compression service centers for this purpose.
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© CS Dept Va Tech, 1998. |
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