Advanced video coding (H.26L)
The long-term objective of the ITU-T video coding experts group under the advanced video coding project is to provide a video coding recommendation to perform substantially better than the existing standards (e.g. H.263+) at very low bit rates. The group worked closely with the MPEG-4 experts group of ISO/IEC for more than six years (from 1997 to 2002). The joint work of the ITU-T and the ISO/IEC is currently called H.26L, with L standing for long-term objectives. The final recommendations of the codec will be made available in 2003, but here we report only on what are known so far. These may change over time, but we report on those parts that not only look fundamental to the new codec, but are also more certain to be adopted as recommendations. The codec is expected to be approved as H.264 by the ITU-T and as MPEG-4 part 10 (IS 14496-10) by ISO/IEC [7].
Simulation results show that H.26L has achieved substantial superiority of video quality over that achieved by the existing most optimised H.263 and MPEG-4 codecs [23]. Most notable features of the H.26L are:
Up to 50 per cent in bit rate saving: compared with the H.263+ (H.263V2) or MPEG-4 simple profile (see Chapter 10), H.26L permits an average reduction in bit rate of up to 50 per cent for a similar degree of encoder optimisation at most bit rates. This means that H.26L offers consistently higher quality at all bit rates including low bit rates.
Adaptation to delay constraints: H.26L can operate in a low delay mode to adapt telecommunication applications (e.g. H.264 for videoconferencing), while allowing higher processing delay in applications with no delay constraints such as video storage and server-based video streaming applications (MPEG-4V10).
Error resilience: H.26L provides the tools necessary to deal with packet loss in packet networks and bit errors in error-prone wireless networks.
Network friendliness: the codec has a feature that conceptually separates the video coding layer (VCL) from the network adaptation layer (NAL). The former provides the core high compression representation of the video picture content and the latter supports delivery over various types of network. This facilitates easier packetisation and better information priority control. | 
