Rate Scalable Video Compression Based on Flexible Block Wavelet Coding Technique

Rate scalable video compression techniques are very attractive, because they are able to encode the video in embedded way that makes the decoding process more flexible to the bandwidth changes. Embedded wavelet coding technology plays an important role in this area. Traditional wavelet transforms are globally optimized. It is very efficient to code the natural images where sudden transitions rarely exist. On the other hand, video compression mostly deals with the differences between adjacent frames, also known as delta frames. Unfortunately, commonly used wavelet transforms are not so efficient on delta frame coding. In this paper, we are presenting a new wavelet coding technique – Flexible Block Wavelet Coding (FBWC). It is specially designed for delta frame compression. FBWC not only makes delta frame compression more efficient but also keeps the rate scalability and other scalabilities of wavelet based scalable video compression techniques. Based on this new delta frame compression technique, we have implemented a highly efficient rate scalable video codec. Its overall performance surpasses the video codec based on SPIHT and is comparable to that of H263. Using FBWC, delta frames are compressed in three steps: First, use motion compensation to eliminate the temporal redundancy between adjacent frames and the predicted error frames (PEFs) are generated. Next, the PEFs will be transformed into wavelet domain using Flexible Block Wavelet Transform (FBWT). Finally, zerotree coding mechanism and entropy coder will be used to actually compress the FBWT transformed wavelet coefficients to the target data rate. FBWT is specially designed to deal with the motion compensation boundary discontinuity in PEFs. It consists of a set of biorthogonal wavelet transforms with boundary treatments. For each 16X16 (8X8) block in a PEF, we choose the most suitable wavelet transform from our candidate set according to the block size and the transform level. The picked wavelet transform will be used to do the current level of transform. An FBWT transformed PEF will be rearranged for embedded coding. By using FBWT, we can handle the motion compensation boundary gracefully. Meanwhile all the scalabilities of embedded wavelet coding are still preserved. To show the advantages of FBWC for PEFs, three QCIF H263 test clips (carphone, foreman and mother&daughter) have been chosen for performance comparison. All the sequences are encoded at 10 fps (by coding every third frame) and at 60 kbps. On average, FBWC outperforms SPIHT by more than 1db in PSNR, and under-performs H263+ by less than 0.3db in PSNR.