H.263 is a video compression standard originally designed as a low-bit-rate
compressed format for videoconferencing. It was developed by the ITU-T Video
Coding Experts Group in a project ending in 1995/1996 as one member of the H.26x
family of video coding standards in the domain of the ITU-T, and it was later
extended to add various additional enhanced features in 1998 and 2000.
Smaller additions were also made in 1997 and 2001, and a unified edition was
produced in 2005. The H.263 codec was first designed to be
utilized in H.324 based systems, but it also found use in H.323, H.320, RTSP and
SIP solutions. H.263 is a required video codec in ETSI
3GPP technical specifications for IP Multimedia Subsystem, Multimedia
Messaging Service and Transparent end-to-end Packet-switched Streaming
Service. In 3GPP specifications, H.263 video is usually used in 3GP container
format. H.263 also found many applications on
the internet: much Flash Video content used to be encoded in Sorenson Spark
format. The original version of the RealVideo codec was based on H.263 up
until the release of RealVideo 8. H.263 was developed as an evolutionary
improvement based on experience from H.261, the previous ITU-T standard for
video compression, and the MPEG-1 and MPEG-2 standards. Its first version was
completed in 1995 and provided a suitable replacement for H.261 at all
bit rates. It was further enhanced in projects known as H.263v2, MPEG-4 Part 2
and H.263v3. MPEG-4 Part 2 is H.263 compatible in the sense that basic
"baseline" H.263 bitstreams are correctly decoded by an MPEG-4 Video
decoder. The next enhanced codec developed by
ITU-T VCEG 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. Most new
videoconferencing products now include H.264 as well as H.263 and H.261
capabilities. An even-newer standard format, HEVC, has also been developed by
VCEG and MPEG, and has begun to emerge in some applications.
Versions Since the original ratification of H.263
in March 1996, there have been two subsequent additions which improved on
the original codec by additional optional extensions.
= Version 1 and Annex I= The original version of H.263 specified
the following annexes: Annex A – Inverse transform accuracy
specification Annex B – Hypothetical Reference Decoder
Annex C – Considerations for Multipoint Annex D – Unrestricted Motion Vector
mode Annex E – Syntax-based Arithmetic Coding
mode Annex F – Advanced Prediction mode
Annex G – PB-frames mode Annex H – Forward Error Correction for
coded video signal The first version of H.263 supported a
limited set of picture sizes: 128x96
176x144 352x288
704x576 1408x1152
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. = H.263v2=
H.263v2 is the informal name of the second edition of the ITU-T H.263
international video coding standard. 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. The H.263+ project was
ratified by the ITU in February 1998. It added the following Annexes:
Annex I – Advanced INTRA Coding mode Annex J – Deblocking Filter mode
Annex K – Slice Structured mode Annex L – Supplemental Enhancement
Information Specification Annex M – Improved PB-frames mode
Annex N – Reference Picture Selection mode
Annex O – Temporal, SNR, and Spatial Scalability mode
Annex P – Reference picture resampling Annex Q – Reduced-Resolution Update mode
Annex R – Independent Segment Decoding mode
Annex S – Alternative INTER VLC mode Annex T – Modified Quantization mode
H.263v2 also added support for flexible customized picture formats and custom
picture clock frequencies. As noted above, the only picture formats
previously supported in H.263 had been Sub-QCIF, QCIF, CIF, 4CIF, and 16CIF,
and the only picture clock frequency had been 30000/1001 clock ticks per second.
H.263v2 specified a set of recommended modes in an informative appendix:
= H.263v3 and Annex X= The definition of H.263v3 added three
annexes. These annexes and an additional annex that specified profiles were
originally published as separate documents from the main body of the
standard itself. The additional annexes specified are:
Annex U – Enhanced reference picture selection mode
Annex V – Data-partitioned slice mode Annex W – Additional supplemental
enhancement information specification Annex X – Profiles and levels definition
The prior informative Appendix II was obsoleted by the creation of the
normative Annex X. In June 2001, another informative
appendix was approved. It describes techniques for encoding and for
error/loss concealment by decoders. In January 2005, a unified H.263
specification document was produced. In August 2005, an implementors guide
was approved to correct a small error in the seldom-used Annex Q
reduced-resolution update mode. Open-source implementation
In countries without software patents, H.263 video can be legally encoded and
decoded with the free LGPL-licensed libavcodec library which is used by
programs such as ffdshow, VLC media player and MPlayer.
See also H.262/MPEG-2 Part 2
References External links
The ITU-T specification for H.263 IETF AVT Working Group - Group that
reviews codec packetizations for RTP RFC 4629 - RTP Payload Format for ITU-T
Rec. H.263 Video RFC 2429 - RTP Payload Format for the
1998 Version of ITU-T Rec. H.263 Video RFC 2190 - RTP Payload Format for H.263
Video Streams H.263 - MultimediaWiki
Intel Integrated Performance Primitives H.263 implementation in vic