H.264

H.264, also known as  MPEG-4 part 10, AVC, and by additional names (see below), is a standard for video compression and one of the most widely used HD video formats. Software routines which implement standards such as this one are known as "codecs" (for "coder-decoders") because the encode and decode video data. They are an essential part of any system that plays or creates digital videos, and can be a component of systems that deal with all sorts of file formats that use a particular standard for encoding or compression as a part of their format.

H.264 is controversial for being patent-encumbered, and hence subject to royalty requirements. In 2013, Cisco is attempting to partially remedy this by producing a freely distributed executable H.264 codec for many platforms for which they have paid the royalty, allowing anybody to download and use it in unmodified form royalty-free. The source code is also openly available, but any altered versions that anybody might create from it would require separate licensing, as would any distribution of the executables other than direct download from Cisco. Thus, the only way to use it as part of a product without additional license fees is to have the product's installer download the executable from Cisco during the install process, rather than including it directly in your own product (whether on disk or downloadable from your site).

HEVC (H.265) has been developed as a more efficient successor to this format, but it is also patent-encumbered. Attempts to create a royalty-free alternative include AV1, Daala, VP9, and Thor.

The H.264 specification does not, in an extremely strict sense, define a codec which fits into a series of bytes; instead, it describes the stream as fitting into a sequence of frames called "network abstraction layer units", which can then be delineated into a raw byte format by the user. The format for putting these into a raw bytestream described by Annex B of the specification apparently is apparently very widely-used. (See the Multimedia Wiki entry.)

Additional Names
This information is from the Multimedia Wiki.
 * ISO/IEC 14496-10
 * ITU-T Recommendation H.264
 * MPEG-4 AVC
 * MPEG-4 ("in the broadcasting world", where a dangerous shortening of the technical name apparently occurs; this usage also might be taken as referring to MPEG-4 Part 2)
 * Joint Video Team, abbreviated JVT
 * H.26L

Specs

 * H.264 official specification page

Software

 * x264
 * OpenH264

Commentary

 * Comments on Cisco, Mozilla, and H.264
 * More commentary
 * Towards a post-H.264 world
 * Google sticks with VP8, opposes Cisco’s push to make H.264 the default codec for WebRTC
 * Will a file encoded with the libx264 play on Windows 8?