Design of a High Speed CAVLC Encoder and Decoder with Parallel Data Path

Variable length coding (VLC) is very suitable for regular data and efficient to compress data without any loss. VLC uses shorter bits of codewords instead of data occurring frequently, but uses the longer bits of codewords instead of data occurring infrequently. It is used in MPEG – 1/2/4 and H.26X (video and image compression standards). The entropy decoder in MPEG-4 AVC/H.264 baseline standard adopts Content Adaptive Variable Length Decoder (CAVLD). Because of symbol-to-symbol dependency, a traditional CAVLC decoder consumes lots of clock cycles in decoding and brings down the performance. We discover the decoding of two parameters spending almost eighty percent of computing time through profiling the computation of sub-modules and analyzing the encoding rules, which are non-zero coefficient (Level) and run_before. Thus this paper proposes a fast algorithm adapted for run_before decoder and the parallel architecture for level decoder, to improve the decoding performance. According to the features of these two methods, we name these two new methods as MLD (Multiple Level Decoding) and NZS (Non-Zero Skipping for run_before decoding). By performing parallel operation on level decoder, MLD can decode two levels in one cycle at most situations, and NZS can produce several values of run_before in the same cycle. These two methods have the advantages of low complexity and regularity design. Keywords-CAVLC Encoder, Decoder, H.264.