[12][15] The next enhanced format developed by ITU-T VCEG (in partnership with MPEG) after H.263 was the H.264 standard, also known as AVC and MPEG-4 part 10.
As H.264 provides a significant improvement in capability beyond H.263, the H.263 standard is now considered a legacy design that is only used for compatibility with older products.
Even newer standard formats, HEVC and VVC, have also been developed by VCEG and MPEG, and have begun to replace H.264 in some applications.
The original version of H.263 specified the following annexes: The first version of H.263 supported a limited set of picture sizes: In March 1997, an informative Appendix I describing Error Tracking – an encoding technique for providing improved robustness to data losses and errors, was approved to provide information for the aid of implementers having an interest in such techniques.
It retained the entire technical content of the original version of the standard, but enhanced H.263 capabilities by adding several annexes which can substantially improve encoding efficiency and provide other capabilities (such as enhanced robustness against data loss in the transmission channel).
In August 2005, an implementors' guide was approved to correct a small error in the seldom-used Annex Q reduced-resolution update mode.
[citation needed] Open-source implementations include the LGPL-licensed libavcodec library (part of the FFmpeg project) which is used by programs such as ffdshow, VLC media player and MPlayer.