一种基于H.264的任意比例空间分辨率转码中的快速宏块类型选择方案

Fast macroblock mode decision for arbitrary downsizing video transcoder based on H.264

在基于H.264的空间分辨率转码中,原有的宏块类型不再适用,从而需要重新选择。提出了一种快速的宏块类型选择方案,适用于基于H.264的任意比例因子的空间分辨率转码。由于任意比例因子的空间分辨率转码中,待编码帧中的宏块无法与已编码帧的宏块边界对齐,提出了影射块和覆盖块的概念,根据缩放因子的大小,在基于块统计和基于像素统计之间作出调整,从而在保证压缩性能的同时,尽可能地降低了运算复杂度。在帧间模式选择部分,对SKIP类型的选择进行了分析,提出SKIP类型的选择与已编码帧中SKIP类型的比例有关,并给出了解决方法。最后针对各种测试序列,并组合了多个图像缩放因子,进行了大量的实验。在帧内模式选择部分,与全搜索法相比,在保证PSNR损失不超过0.1dB的前提下,方法的速度能提高约3.5倍;在帧间模式选择部分,与全搜索法相比,在保证PSNR损失不超过1.0dB的前提下,本方法的速度能提高约30倍。

In spatial resolution transcoder based on H.264, the pre-encoded macroblock modes are not suitable anymore. This paper proposed a fast macroblock mode decision method in arbitrary downsizing video transcoder based on H.264. In spatial resolution transcoder with arbitrary factor, the responding area in pre-encoded frames for macroblocks to be re-encoded was not aligned with the boundary of macroblock. It proposed the concepts of mapping block and covering block. To reduce the computation complexity, method based on blocks or based on pixels was adopted according to different downsizing factor. In inter-prediction mode decision part, analyzed SKIP mode specially. The percentage of SKIP mode in pre-encoded frame was considered in the proposed scheme to decide SKIP mode in frame to be re-encoded. It compared the PSNR performance and computation complexity of proposed method with the full search algorithm by extensive experiments. For the intra-frame mode decision part, the proposal achieves about 3.5 times improvement in computation complexity comparing to full search algorithm while the maximum PSNR is degraded by about 0.1 dB. For the inter-frame mode decision part, the proposal achieves about 30 times improvement in computation complexity while the maximum PSNR is degraded by about 1.0 dB.