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H.263 Video Coding

H.263 is a standard videoconferencing codec. It was published in February 1995 and has been designed for low-bitrate communication. It is used primarily for applications with datarates less than 64Kbits/s, but later this limitation was removed. H.263 was designed as an improvement over H.261, the previous codec for video compression published by ITU-T, and the MPEG-1 and MPEG-2 standards.

The coding algorithm of H.263 is the coding algorithm of H.261 with some improvements about performance and error recovery. For example H.263 uses half pixel precision for motion compensation, whereas H.261 used full pixel precision and a loop filter. As a result lots of parts of the hierarchical structure are now optional, so the standard can be configured for lower datarate or better error recovery.

H.263 supports five resolutions, contrary to H.261 which supports only two: QCIF and CIF. In addition to QCIF and CIF, there is SQCIF, 4CIF, and 16CIF. SQCIF, 4CIF and 16CIF are half, 4 and 16 times the resolution of CIF respectively.

The drawback is that H.263 is CPU intensive, so it can’t be used with datarates higher than 50Kbps nor play on lower-end machines.

Finally it should be noted that H.263 has a strong temporal compression component and works better on movies where changes between frames aren’t big.In our days, H.263 has replaced H.261 in the field of videoconferencing in most applications and also it is used for Internet video streaming. The most important features of H.263 are presented in the following table.

Ideal source materialLow motion video
Supported bit depths16-bit color
Compression timeSymmetrical, realtime
Temporal compression?Yes
Special features-
Encoder requirementsAny MacOS or Windows
Decoder requirementsPowerMac or Pentium
Encoder availabilityBuilt into QuickTime 3
Decoder availabilityBuilt into QuickTime 3
AlgorithmDiscrete Cosine Transform (DCT)
with Motion Compensation based on H.261
ManufacturerMany, including Apple, Microsoft, Vivo

For more information visit: H.263 - Wikipedia, the free encyclopedia and H.263 Video Coding

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