Comparison of the Coding Efficiency of Video Coding Standards—Including High Efficiency Video Coding

该文比较了HEVC、H.264/MPEG-4 AVC、H.263、MPEG-4和H.262/MPEG-2的编码性能。
比较不同编码标准的编码器的性能，一个比较麻烦的问题是：编码配置和优化技术难以统一。编码配置包括参考帧个数、GOP结构、QP偏置等等。还有各个编码器的优化技术可能各有不同，包括运动估计算法、失真度量、lambda的计算，也会影响最终的实验结果。这两方面的问题都是比较棘手的，要想在这两方面均统一，需要改各个编码器的配置文件和代码。要想把这个数据测出来，实验的工作量还是很大的。
至于编码标准的制定者为什么要给编码器这么大的自由度，文章中解释了：
When designing a video coding standard for broad use, the standard is designed in order to give the developers of encoders and decoders as much freedom as possible to customize their implementations. This freedom is essential to enable a standard to be adapted to a wide variety of platform architectures, application environments, and computing resource constraints. This freedom is constrained by the need to achieve interoperability, i.e., to ensure that a video signal encoded by each endor’s products can be reliably decoded by others. This is ordinarily achieved by limiting the scope of the standard to two areas (cp. [11, Fig. 1]).
值得注意的几点：
1、HEVC相对于H.264/AVC，interactive applications配置下比entertainment applications下的增益大。
2、interactive applications配置下，H.263 CHC相比于MPEG-4 ASP有13.2%的编码增益；而entertainment applications配置下，MPEG-4 ASP相比于H.263 HLS有3.9%的增益。这两条实验数据符合H.263和MPEG-4的定位（应用场景）。
3、该文测的H.263是H.263v3，即H.263++。
4、”each conforming MPEG-4 decoder must be capable of decoding H.263 Baseline bitstreams (i.e., bitstreams that use no H.263 optional annex features)”。
5、In contrast to previous standards, the inverse transforms are specified by exact integer operations, so that, in error free environments, the reconstructed pictures in the encoder and decoder are always exactly the same.