Vcodex

H.264 quantization parameter

2009-04-04T18:23:00.002Z

Quantization in an H.264 encoder is controlled by a quantization parameter, QP, that ranges from 0 to 51. QP is an index used to derive a scaling matrix. It is possible to calculate the equivalent quantizer step size (Qstep) for each value of QP (see my tutorial on H.264 4x4 transform). As QP increases, Qstep increases; in fact, Qstep doubles for every increase of 6 in QP. The logarithmic relationship can be seen in this graph of QP (x-axis, linear) vs. Qstep (y-axis, logarithmic).

Guest lectures

2009-03-31T08:30:00.003Z

I will be giving a number of guest lectures on video coding over the next few months, in Rochester (NY), Aberdeen (UK), France and Spain. You can find out about arranging a lecture on H.264/AVC, video codec design and optimization, or emerging video coding topics, by visiting this page.

Modified transform tutorial

2009-03-04T08:22:00.001Z

I have modified the tutorial on the H.264 4x4 transform and quantization processes and corrected a minor error. The new tutorial is available here.

H.264 vs MJPEG2000 vs MJPEG

2009-01-27T12:23:00.003Z

Here's an interesting article:

http://www.isc365.com/Why_We_Like_MJPEG_Compression.aspx

It's interesting because it claims that MJPEG is better than H.264. This is a strange claim. If you want to do Intra-only coding (i.e. no motion compensation), you can use H.264 in Intra mode. Detlev Marpe demonstrated that H.264 in Intra mode has similar performance to Motion JPEG2000:
http://www.f4.fhtw-berlin.de/~barthel/paper/spie03_marpe_et_al.pdf

Note that Marpe includes actual results, unlike the article above. So, even in Intra mode, H.264 will significantly out-perform the older MJPEG standard. Using Intra and Inter coding (i.e. adding motion compensation) will increase the performance dramatically, even if there is a lot of camera movement and detail in the scene.

If in doubt about competing claims, ask for rate-distortion results and independent subjective test results. For example, see this site for some third-party codec comparisons:
http://compression.ru/video/codec_comparison/mpeg-4_avc_h264_2007_en.html

Or send me an email - I will try and answer it and give you an impartial opinion.

- Iain.

Analyzing H.264 clips

2009-01-20T13:01:00.003Z

I have put two examples of H.264 coded sequences on the downloads page. Both are short segments of the "Foreman" CIF video sequence, coded using the Baseline and Main profiles of H.264.

Use a viewer such as Elecard's Streameye to analyze the clips:

http://www.elecard.com/products/products-pc/professional/streameye/
(you can download a time-limited trial version).

Here's an screenshot of the Main Profile clip. You can see the P-slices (blue bars) and B-slices (green bars). Use the Streameye menus to examine frames, look at the distribution of macroblock types, motion vectors, etc.

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

2009-01-20T10:52:00.002Z

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

New tutorial on transform and quantization

2009-01-08T09:41:00.001Z

New white paper / tutorial posted on the derivation of the 4x4 forward + inverse transforms. Comments welcome. - Iain.

Fully Configurable Video Coding

2008-09-25T07:32:00.003Z

I gave a plenary talk at IEEE System on Chip Conference last week and used the opportunity to launch our new research topic, Fully Configurable Video Coding. The idea is to enable complete, dynamic reconfiguration of a video codec. The new concept is attracting a lot of interest from industry and researchers. Here's some more information.

Article on video compression patents

2008-03-27T14:52:00.002Z

I've posted a new article on video compression patents and IPR. The article gives an overview of the IPR position related to video coding and video compression, with particular reference to video coding standards and patent licenses.

New version of H.264/AVC overview

2007-12-03T14:52:00.001Z

I have posted a new version of my introductory overview, "What is H.264?". Visit the page and please contact me with any comments.

Computer-drawn or hand-drawn diagrams ?

2007-11-01T10:33:00.000Z

I'm developing diagrams for a new edition of my book on H.264/AVC. I've been experimenting with hand-drawn vs. computer-drawn diagrams. I quite like the immediacy of hand-drawn diagrams. Here are a few examples - I'd like to have your opinions on these. Please leave a comment (or send me an email) with your views - do you prefer hand-drawn or computer-drawn?

The examples are in this file:
Figures_H264book_poll.pdf

New overview of H.264/AVC

2007-03-29T10:27:00.000Z

I have written a new white paper that gives an overview of the H.264/AVC standard (here). It's intended to be a (relatively) non-technical introduction to the standard. The new paper describes what H.264 is, how an H.264 video codec works and why H.264 is an important industry standard. I'd be happy to receive any comments.

Topics for new tutorials

2007-03-06T10:47:00.000Z

I will be posting a number of new H.264 tutorials over the next few months. I plan to update the existing tutorials (here) and add further topics. The first will be an "easy" introduction to the H.264/AVC standard. I'd welcome requests for new tutorial topics, so please add a comment if you'd like to suggest a topic for a tutorial paper.
- Iain

Welcome

2007-02-27T09:07:00.000Z

Welcome to the newly-published Vcodex site. This site contains resources, links and information about video compression and about my work. I have kept the existing resources (including the popular H.264 tutorials) and added new material. I will continue to add resources to the site. Contact me if you'd like to suggest or request further resources, tutorial topics, etc, or to find out more about what I do.