ITU-T H.264, Advanced Video Coding for Generic Audiovisual Services – Coding of Moving Video, also published as ISO/IEC 14496-10 (MPEG-4 Part 10),

Advanced Video Coding.

H.264 is usually pronounced

H-dot-TWO-SIX-FOUR.

Compounding 1.06 twelve times yields a factor of two:

1.0612 ≈ 2

H.264 denotes a codec standardized by ITU-T (under the designation H.264) and by ISO/IEC (under the designation MPEG-4 Part 10). The Simple Studio Profile (SStP) of MPEG-4 Part 2 is used in hdcam. That aspect of Part 2, and all of Part 10, are applicable to broadcastquality video; other than those cases, MPEG-4 is generally not applicable to broadcast-quality video. H.264 was developed by the Joint Video Team (JVT), where it was referred to as Advanced Video Coding (AVC); its ITU-T nomenclature during development was H.26L. All of these terms were once used to denote what is now, after adoption of the standard, best called H.264.

H.264 is broadly similar to MPEG-2, but the “low fruit” had been taken. Compression improvements in H.264 are obtained by a dozen or so techniques, each having perhaps 6% improvement in coding efficiency – but a dozen of those cascaded yields twice the efficiency of MPEG-2. (Practitioners claim efficiency as low as 1.5 and as high as 3 times that of MPEG-2.) H.264 spans a wide range of applications, from surveillance video, to video conferencing, to mobile devices, to internet video streaming, to HDTV broadcasting.

H.264 is complicated. The standard (in its 2010-03 edition) comprises 669 pages of very dense description. Implementing an encoder or decoder takes many manyears. Software, firmware, and hardware implementations are commercially available. Even hardware implementations require embedded firmware: H.264 VLSI solutions typically involve one or more embedded RISC processors and quite a bit of associated firmware.

MPEG LA, L.L.C. is not affiliated with MPEG (the standards group). LA apparently stands for Licensing Administration. The organization is based in Denver, not Los Angeles.

The H.264 features that extend MPEG-2 are described in the remaining sections of this chapter.

I assume that you are familiar with Introduction to video compression, on page 147, and with JPEG, M-JPEG, DV, and MPEG-2, described in the preceding three chapters.

Like MPEG-2, H.264 specifies exactly what constitutes a conformant bitstream: A conformant (“legal”) encoder generates only conformant bitstreams; a legal decoder correctly decodes any conformant bitstream. H.264 effectively standardizes the behaviour of

a decoder, but does not standardize the encoder!

The goal of compression is to reduce data rate while minimizing the visibility of artifacts. The best way – most experts say, the only way – to establish the performance of an encoder is to visually assess the result of compressing and decompressing video streams.

H.264 is covered by hundreds of patents. Implementors, manufacturers, users, and/or others may or may not be required to take out a licence to the “patent pool” administered by MPEG LA.

Not all features of H.264 are expected to be implemented in every decoder; for example, B-slices (comparable to MPEG-2 B-pictures) are prohibited in the baseline profile. Applications have various bit rates, and decoders can have various levels of resources (e.g., memory); like MPEG-2, a system of profiles and levels determines the minimum requirements.

Algorithmic features, profiles, and levels

Table 48.1 opposite summarizes the algorithmic features of H.264 beyond MPEG-2. The features in the top section are available in all profiles; features in the sections below are profile-dependent.

The features available in the baseline and extended profiles concern robust handling of data conveyed across unreliable channels. These features (and profiles) are generally not of interest for professional video, and they are not permitted in the main and high profiles.

The features of the extended, main, and high profiles offer improved coding efficiency. CABAC improves the performance of variable-length entropy coding.

Fidelity range extensions (FRExt) refers to several algorithmic features incorporated into the high profiles – HiP, Hi10P, Hi422P, and Hi444P – to enable