The Video Coding Experts Group or Visual Coding Experts Group (VCEG, also known as Question 6) is a working group of the ITU Telecommunication Standardization Sector (ITU-T) concerned with video coding standards. It is responsible for standardization of the "H.26x" line of video coding standards, the "T.8xx" line of image coding standards, and related technologies.
Administratively, VCEG is the informal name of Question 6 (Visual coding) of Working Party 3 (Media coding) of ITU-T Study Group 16 (Multimedia coding, systems and applications). Its abbreviated title is ITU-T Q.6/SG 16.
The goal of VCEG is to produce recommendations (international standards) for video coding and image coding methods appropriate for conversational (e.g. videoconferencing and video telephony) and non-conversational (e.g., streaming, broadcast, file download, media storage/playback, or digital cinema) audio/visual services. This mandate concerns the maintenance and extension of existing video coding recommendations, and laying the ground for new recommendations using advanced techniques to significantly improve the trade-offs between bit rate, quality, delay, and algorithm complexity. Video coding standards are desired with sufficient flexibility to accommodate a diverse number of transport types (Internet, LAN, Mobile, ISDN, GSTN, H.222.0, NGN, etc.).
Question 6 is part of Study Group 16, which is responsible for studies relating to multimedia service capabilities, and application capabilities (including those supported for NGN). This encompasses multimedia terminals, systems (e.g., network signal processing equipment, multipoint conference units, gateways, gatekeepers, modems, and facsimile), protocols and signal processing (media coding).
VCEG was preceded in the ITU-T (which was called the CCITT at the time) by the "Specialists Group on Coding for Visual Telephony" chaired by Sakae Okubo (NTT) which developed H.261. The first meeting of this group was held Dec. 11–14, 1984 in Tokyo, Japan. Okubo was also the ITU-T coordinator for developing the H.262/MPEG-2 Part 2 video coding standard and the requirements chairman in MPEG for the MPEG-2 set of standards.
The first digital video coding standard was H.120, created by the CCITT (now ITU-T) in 1984. H.120 was not usable in practice, as its performance was too poor. H.120 was based on differential pulse-code modulation (DPCM), which had inefficient compression. During the late 1980s, a number of companies began experimenting with the much more efficient discrete cosine transform (DCT) compression for video coding, with the CCITT receiving 14 proposals for DCT-based video compression formats, in contrast to a single proposal based on vector quantization (VQ) compression. The H.261 standard was subsequently developed based on DCT compression.
In 1994, Richard Shaphorst (Delta Information Systems) took over new video coding development in ITU-T with the launch of the project for developing H.324. Schaphorst appointed Karel Rijkse (KPN Research) to chair the development of the H.263 video coding standard as part of that project. In 1996, Schaphorst then appointed Gary Sullivan (PictureTel, since 1999 Microsoft) to launch the subsequent "H.263+" enhancement project, which was completed in 1998. In 1998, Sullivan was made rapporteur (chairman) of the question (group) for video coding in the ITU-T that is now called VCEG. After the H.263+ project, the group then completed an "H.263++" effort, produced H.263 Appendix III and H.263 Annex X, and launched the "H.26L" project with a call for proposals issued in January 1998 and a first draft design adopted in August 1999. In 2000, Thomas Wiegand (Fraunhofer HHI) was appointed as an associated rapporteur (vice-chairman) of VCEG. Sullivan and Wiegand led the H.26L project as it progressed to eventually become the H.264 standard after formation of a Joint Video Team (JVT) with MPEG for the completion of the work in 2003. (In MPEG, the H.264 standard is known as MPEG-4 part 10.) Since 2003, VCEG and the JVT have developed several substantial extensions of H.264, produced H.271, and conducted exploration work toward the potential creation of a future new "HEVC". In January 2010, the Joint Collaborative Team on Video Coding (JCT-VC) was created as a group of video coding experts from ITU-T Study Group 16 (VCEG) and ISO/IEC JTC 1/SC 29/WG 11 (MPEG) to develop a new generation video coding standard.
In July 2006, the video coding work of the ITU-T led by VCEG was voted as the most influential area of the standardization work of the CCITT and ITU-T in their 50-year history. The image coding work that is now in the domain of VCEG was also highly ranked in the voting, placing third overall.
In May 2015 the ITU celebrated its 150-year anniversary, and the work of VCEG was one of the five areas of standardization to be recognized by an "ITU 150 Award" as one of the most influential topics of ITU work.
Video coding standards
The organization now known as VCEG has standardized (and is responsible for the maintenance of) the following video compression formats and ancillary standards:
- the first digital video coding standard. v1 (1984) featured conditional replenishment, differential PCM (DPCM), scalar quantization, variable-length coding and a switch for quincunx sampling. v2 (1988) added motion compensation and background prediction. This standard was little-used and no codecs exist.
- was the first practical digital video coding standard (late 1990). This design was a pioneering effort, based on motion-compensated discrete cosine transform (DCT) coding. All subsequent international video coding standards have been based closely on its design. MPEG-1 Part 2 was heavily influenced by this.
- it is identical in content to the video part of the ISO/IEC MPEG-2 Part 2 standard (ISO/IEC 13818-2). This standard was developed in a joint partnership between VCEG and MPEG, and thus it became published as a standard of both organizations. ITU-T Recommendation H.262 and ISO/IEC 13818-2 were developed and published as "common text" international standards. As a result, the two documents are completely identical in all aspects.
- was developed as an evolutionary improvement based on experience from H.261, 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 bitrates. MPEG-4 Part 2 is substantially similar to this.
- also known as H.263+ or as the 1998 version of H.263, is the informal name of the second edition of the H.263international video coding standard. It retains the entire technical content of the original version of the standard, but enhances H.263 capabilities by adding several annexes which substantially improve encoding efficiency and provide other capabilities (such as enhanced robustness against data loss in the transmission channel). The H.263+ project was completed in late 1997 or early 1998, and was then followed by an "H.263++" project that added a few more enhancements in late 2000.
- Advanced Video Coding (AVC) is the most widely used standard in the series of international video coding standards. It was developed by a Joint Video Team (JVT) consisting of experts from ITU-T's Video Coding Experts Group (VCEG) and ISO/IEC's Moving Picture Experts Group (MPEG) created in 2001. The ITU-T H.264 standard and the ISO/IEC MPEG-4 Part 10 standard (formally, ISO/IEC 14496-10) are technically identical. The final drafting work on the first version of the standard was completed in May 2003. As has been the case with past standards, its design provides a balance between the coding efficiency, implementation complexity, and cost based on state of VLSI design technology (CPUs, DSPs, ASICs, FPGAs, etc.).
- H.264.1: Conformance testing for H.264
- H.264.2: Reference software for H.264
- High Efficiency Video Coding (HEVC) was completed in January 2013 for its first edition. HEVC has approximately twice the compression capability of its H.264/MPEG-4 AVC predecessor and was similarly developed with MPEG in a joint team known as the Joint Collaborative Team on Video Coding (JCT-VC). It is also standardized as ISO/IEC 23008-2 (MPEG-H Part 2).
- Video back channel messages for conveyance of status information and requests from a video receiver to a video sender
Image coding standards
Starting in late 2006, VCEG has also been responsible for the ITU-T work on still image coding standards including the following:
- JPEG (ITU-T T.80, T.81, T.83, T.84, T.86, T.871, and T.872) and the JPEG-like ITU-T T.851
- JBIG-1 (ITU-T T.80, T.82 and T.85)
- JBIG-2 (ITU-T T.88 and T.89)
- JPEG-LS (ITU-T T.87 and T.870)
- JPEG 2000 (ITU-T T.800 through T.813)
- JPEG XR (ITU-T T.832, T.833, T.834, T.835, and T.Sup2)
- MRC (ITU-T T.44)
- ITU Telecommunication Standardization Sector
- Joint Photographic Experts Group (JPEG)
- Moving Picture Experts Group (MPEG)
- Gary Sullivan (engineer)
- Video codec
- Video compression
- Video quality
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