Single-pass constant- and variable-bit-rate MPEG-2 video compression

Most real-time MPEG-2 encoders are designed to perform in a constant-bit-ra te (CBR) mode, in which buffer constraints are imposed to circumvent large deviations from a desired rate at any instant in time. Although such stream s are generally good-quality sequences, certain types of operations or envi ronments call for a more efficient real-time CBR encoder. The first part of the paper describes how a better-quality CBR video stream can be produced by estimating the relative complexity of a picture in comparison with the a verage complexity of the partially encoded stream and using it to adjust th e compression parameters in a single-pass mode of operation. Our CBR encode r is particularly attractive for digital broadcast and editing environments , in which representations of higher-fidelity video objects in both display and freeze modes are constantly pursued. The second part of the paper desc ribes the real-time generation of video streams with a variable-bit-rate (V BR) encoder. This mode of operation is highly desirable for home entertainm ent and recreational events. We propose a robust single-pass VER video enco der algorithm which is capable of learning and adapting itself to the compl exity of image segments and thereafter creating streams which have constant visual picture quality. The new VER scheme displays a better performance t han the CBR encoder, particularly when special effects such as scene transi tions, fades, or luminance changes are to be compressed. Both CBR and VER e ncoders are fully compliant with the MPEG-2 standard and are easily impleme ntable with IBM encoder architecture. Compression results for the new singl e-pass encoding algorithms and comparisons with previous CBR schemes are pr ovided. The result suggests the suitability of our VER approach for record/ playback in storage media such as digital video disc (DVD) players, disk-ba sed camcorders, and digital videocassette recorders (DVCRs). It further ref lects the importance of our single-pass CBR scheme for providers of broadca st services, for which it allows more video programs to be allocated to a s elected communication link, and for in-studio applications, for which it gr eatly facilitates visual analysis of captured streams.