The analysis and modelling of hybrid coded VBR video

A basic hybrid motion compensation/differential pulse code modulation/discrete cosine transform (MC/DPCM/DCT) video coding algorithm has been adopted for various video coding standards such as H.261, H.263, MPEG-1 and MPEG-2. Although currently recommended codec implementations by these standards are basically constant bit rate (CBR), it is essentially a variable bit rate (VBR) coding method. The introduction of a smoothing buffer for codecs provides CBR output streams, which can be transmitted conveniently through the current communication network. However, the constant bit rate output results in degradation of coded picture quality. It is important that the output bit rate is made variable to achieve high and constant picture quality. This paper analyses and makes a suggestion for the modelling of output bit streams from an MPEG committee endorsed MPEG-2 encoder. VBR is achieved by ignoring the output smoothing buffer