Tuesday, January 20, 2009

What does the "H" in H.264 stand for?

I was asked this question today and I think it's a really good question: what does the "H" stand for in H.264 ?

H.264 is an ITU standard or "Recommendation". ITU Recommendations are
assigned letters and numbers; so everything that starts with H. is in
a similar area (audiovisual/multimedia) :
http://www.itu.int/rec/T-REC-h

Other groups of standards start with different letters, always a
letter and a number. E.g. P.910 is a standard for subjective quality measurement.

ISO/IEC standards have numbers, so MPEG-2 Video is ISO/IEC 13818-2. "MPEG" is a standardisation group within ISO/IEC.

H.264 is co-published with ISO/IEC MPEG so it also has an MPEG number. Confusingly,
it's given the same basic number as MPEG-4:

  • MPEG-4 Visual (older standard) is ISO/IEC 14496-2 ("MPEG-4 Part 2")
  • H.264/Advanced Video Coding is co-published as ISO/IEC 14496-10 ("MPEG-4 Part 10")

A list of a few current standards:
http://www.citeulike.org/user/xistenshal/tag/standard

Finally, a note about the publication date of standards. The ISO/IEC or ITU website lists the date of the most recent published version of a standard. However, this can be confusing. For example, ITU-T H.263 was first published in 1995, but the most recent updated version was published in 2005 (after the first publication of H.264). Generally, updated versions will correct errors in the text and (in some cases) add extensions. For a realistic timeline of standards development, look at the original publication date. In chronological order of original publication date:
  • H.261
  • MPEG-1
  • MPEG-2 / H.262 (co-published)
  • H.263
  • MPEG-4 Visual
  • H.264 / MPEG-4 Part 10 (co-published)
  • VC-1

1 comment:

compressionist said...

Are there any reference codec for mpeg-2 in the public domain?