Design of an H.264/AVC Decoder with Memory Hierarchy and Line-Pixel-Lookahead

This paper describes a novel memory hierarchy and line-pixel-lookahead (LPL) for an H.264/AVC video decoder. The memory system is the bottleneck of most video processors, particularly in the newly announced H.264/AVC. This is because it utilizes the neighboring pixels to create a reliable predictor, leading to a dependency on a long past history of data. This problem can be resolved by allocating memory space but inducing large silicon area and power consumption as well. We first review the existing solutions and propose a three-level memory hierarchy with line-pixel-lookahead to improve access efficiency. Three-level memory hierarchy includes registers, content/slice SRAM and external frame DRAM. We emphasize the need to consider the secondary hierarchy, content/slice SRAM, during the design of an H.264/AVC decoder. Specifically, we introduce a slice SRAM and line-pixel-lookahead to lower the memory capacity and external bandwidth. This SRAM stores neighboring pixels and prevents the data re-access from DRAM. Linepixel-lookahead exploits multi-dimensional pixel locality so as to averagely improve prediction performance by 6.54% compared to conventional vertical prediction. Simulation results also reveal that the proposal makes a better trade-off between memory allocation and external bandwidth as well as power, leading to 50% of memory power reduction compared to the design without exploiting the secondary slice SRAM hierarchy.