Improved encoding of DCT coefficients for low bit-rate video coding using multiple VLC tables

All current video compression standards employ motion compensated prediction and blockwise encoding of the prediction error using the discrete cosine transform (DCT). The DCT coefficients of each block are quantized, re-ordered into a vector, and each zero-run/coefficient pair is encoded as a single symbol, using a variable length code (VLC) table. In this paper, we show that the use of multiple instead of one VLC table yields significant bit-rate savings of the coded sequences, compared to H.263. The bit-rate-savings are typically up to 20% for medium bit-rates and still around 5% for very low bit-rates. No extra information has to be transmitted. The complexity at both coder and decoder is practically not increased. The only disadvantage of the method is the need to store larger VLC tables.