ABSTRACT
This chapter introduces ITU-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, discusses the technical improvements with which H.263 achieves high coding efficiency and also presents features of H.263+, H.263++, and H.26L. In parallel with the International Standards Organization /International Electrotechnical Commission development of the Moving Picture Experts Group-1/2 standards, the ITU-T has developed H.261 for video-telephony and video-conferencing applications in an ISDN environment. Very-low-bit-rate video coding has found many industry applications such as wireless and network communications. The key technologies used in the H.261 video coding standard are the discrete cosine transform and motion compensation. The H.261 video decoder performs the inverse operations of the encoder. After optional error-correction decoding, the compressed bitstream enters the decoder buffer and then is parsed by the variable-length decoder. The syntax of H.261 video coding has a hierarchical layered structure.
