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The recently completed CCITT H.261 and ISO MPEG1 video
compression standards are based on a hybrid coding technique
which employs motion compensation, spatial-domain discrete
cosine transform, scalar quantization, and Huffman-type coding.
They both specify the syntax of the compressed data stream and
the method of decoding, but leave considerable latitude in the
design of the encoder. We therefore propose a coding approach,
called delayed coding, to overcome some undesirable artifacts
which may accompany typical coding schemes based on simple
buffer-level-feedback control of quantization stepsizes.
Example of such artifacts are buffer over- and underflows and
non-uniform visual quality across different parts of an image.
Our theoretical studies on this approach can be divided into
two broad parts, i.e., (1) the investigation of a general
delayed-coding approach and its constrained optimization and
(2) the development of a particular algorithm for optimal
delayed coding within the H.261 framework based on several
different MSE criteria. Experimental results show that, with
this approach, the compressed video quality can be improved
over typical coding methods. Also, the buffer level can be
perfectly controlled. The basic approach of optimal delayed
coding is applicable to coding algorithms other than H.261 and
MPEG1.
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