ITU-T Video Coding Standards H.261 and H.263
This chapter introduces International Telecommunication Union-T video coding standards H.261 and H.263, which are established mainly for videophony and videoconferencing. It presents the basic technical detail of H.261 and discusses the technical improvements with which H.263 achieves high coding efficiency. The chapter also presents features of H.263+, H.263++, and H.26L. Very low bit rate video coding has found many industrial applications such as wireless and network communications. The H.261 video coding standard has many common features with the Moving Picture Experts Group-1 (MPEG-1) video coding standard. The accuracy of motion compensation in MPEG-1 is up to a half pixel, but only a full pixel in H.261. However, H.261 uses a loop-filter to smooth the earlier frame. The video encoder and video decoder delays of H.261 need to be known to allow audio compensation delays to be fixed when H.261 is used in interactive applications.