A Real-Time H.264/AVC Encoder With Complexity-Aware Time Allocation

摘要

This paper presents a novel processing time control algorithm for a hardware-based H.264/AVC encoder. The encoder employs three complexity scaling methods partial cost evaluation for fractional motion estimation (FME), block size adjustment for FME, and search range adjustment for integer motion estimation (IME). With these methods, 12 complexity levels are defined to support tradeoffs between the processing time and compression efficiency. A speed control algorithm is proposed to select the complexity level that compresses most efficiently among those that meet the target time budget. The time budget is allocated to each macroblock based on the complexity of the macroblock and on the execution time of other macroblocks in the frame. For main profile compression, an additional complexity scaling method called direction filtering is proposed to select the prediction direction of FME by comparing the costs resulting from forward and backward IMEs. With direction filtering in addition to the three complexity scaling methods for baseline compression, 32 complexity levels are defined for main profile compression. Experimental results show that the speed control algorithm guarantees the processing time to meet the given time budget with negligible quality degradation. Various complexity levels for speed control are also used to speed up the encoding time with a slight degradation in quality and a minor reduction of the compression efficiency.