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What is H.263?

Video Format Description

H.263 is a member of the H.26x family of video coding standards designed by ITU (International Telecom Union). It was developed in 1995 as an improvement over H.261, the previous ITU codec.

H.263 has been optimized for a large range of bit rates and not just 64K bits/s like with H.261. Another improvement is that it supports five resolutions. Besides the CIF (Common Interchange Format) and QCIF (Quarter Common Interchange Format) that H.261 supports, it also supports SQCIF, 4CIF, and 16CIF. 4CIF is 4 times the resolution of CIF, and 16CIF is 16 times the resolution. SQCIF is about half the resolution of QCIF. This means that H.261 compares well with the MPEG standards. Other features that make it similar to MPEG are Syntax-based Arithmetic Coding, Unrestricted Motion Vectors, Advance Prediction Mode, alopng with Frame Prediction.

The original H.263 had 8 extensions (or annexes): Inverse Transform Accuracy Specification, Hypothetical Reference Decoder, Syntax-based Arithmetic Coding,Considerations for Multipoint, Unrestricted Motion Vectors, Advance Prediction Mode, Frame Predictions, and Error Corrections.

In 1997, version 2 of H.263 (known as H.263v2 or H.263+) was developed in which some more extensions were added for enhancement. These new extensions were Advanced INTRA Coding; De-blocking Filter Mode; Slice Structured Mode; Supplemental Enhancement Information Specification; Improved Frame Predictions; Reference Picture Selection; Temporal, SNR, and Spatial Scalability; Reference Picture Re-sampling; Reduced-Resolution Update; Independent Segment Decoding; Alternative INTER VLC Mode; and Modified Quantization.

In the year 2000, a still more improved version, known as H.263v3 or H.263++, was developed. This included some additional extensions - Enhanced Reference Picture Selection Mode, Data-partitioned Slice Mode, and Additional supplemental Enhancement Information Specification. In 2001 and 2005 some more modifications were made and the final version was published.

An H.263 video can be played back on LGPL-licensed libav encoded VLC Media and MPlayer multimedia players, Real Video, Windows Media Player, and QuickTime. The H.263 standard is used in video and desk top video conferencing; video telephony; surveillance and monitoring; internet video (like YouTube, MySpace, and Google Video); and creating 3GPP files for playback on mobile phones.