Very low bit rate video codec using variable blocksize
Entropy-constrained Residual · 1997
In this paper we study coding of video sequences at very low bitrates using an entropy-constrained variable block size residual vector quantizer. For a given complex- ity, it is well understood that structured vector quantizers perform better than unstructured and unconstrained vec- tor quantizers. A combination of structured vector quan- tizers is used in this paper to encode the video sequences. The proposed codec uses a Discrete Cosine Transform(DCT) based transform vector quantizer and a variable-rate resid- ual vector quantizer in cascade. The transform-VQ captures the low-frequency information using only a small portion of the bit-budget, while the later stage residual VQ captures the high-frequency information using the remaining bits. A strategy to adaptively refine only areas of high activity us- ing recursive decomposition and selective refinement is used in the later stages. An entropy constraint is used to modify the codebooks to allow better entropy coding of the indices. Performance of the proposed codec is evaluated and com- pared with the H.263 based codec. Experimental results show not only better quantitative performance but also sig- nificantly better perceptual quality. Keywords- Very low bit rate video coding, vector quanti- zation, DCT, variable blocksize.