A very high throughput fully hardwired CABAC decoder

Abstract

Context-based Adaptive Binary Arithmetic Coding (CABAC) in H.264/AVC can achieve high compression ratio at the expense of high computational complexity. We have previously proposed a fully hardwired CABAC decoder that supports real-time QFHD (4x1080HD) decoding at maximum bit rate of 80 Mbps. For higher end applications, we analyze the bin distribution of each Syntax Element (SE) type and the performance of our previous work. The analysis results show that mvd SEs account for significant amount of bins and GetNeighbor (GN) process degrades the utilization of Arithmetic Engine (AE). Therefore, we propose three methods to speed up mvd decoding and increase AE utilization. For mvd SEs, we employ a Two-Bin Arithmetic Engine (TBAE) to decode two mvd bins per cycle. To increase AE utilization, we reduce the cycle-count of the GN process and propose a prediction method to perform AE and GN in parallel. Experimental results show that our new CABAC decoder gives 45% throughput improvement and is capable of decoding QFHD video at maximum bit rate of 221 Mbps when running at 238 MHz.