| Abstract |
This paper presents recent progress of our ongoing research
evaluating the prospects of adaptive vector quantization
(AVQ) for very-low-bitrate video coding. In contrast to
conventional state-of-the-art video coding based on entropy
coding of motion compensated residual frames in the frequency
domain, adaptive vector quantization offers the potential
to adapt its codebooks to the changing statistics of image
sequences. The basic building blocks of our current AVQ
video codec are (1) block-based coding in the wavelet domain
where wavelet coefficients correspond to (overlapping)
spatial regions, (2) hierarchical organization of the wavelet
coefficients using quad-tree structures, (3) three way coding
mode decision for each block (block replenishment, product
code vector quantization, new VQ block with codebook
update), and (4) rigorous rate/distortion optimization for all
coding choices (image partition and block coding mode).
This video codec does not apply motion compensation, however.
A comparison with standard transform coding (H.263)
shows that inspite of the improvements of our coder over previously
published AVQ video coders it still shows a performance
gap of about 1 dB for some test sequences. We conclude
that motion compensation is essential also for codecs
based on AVQ. First preliminary tests show that AVQ coders
that incorporate motion compensation can become competitive
with standard transform coding. |