Image Processing Reference
In-Depth Information
Nevertheless, H.264 has always maintained its lead over MPEG-2 and has, for most of its
life, been twice as efficient.
Envivio has produced H.264 video at 800 Kbps that would be good enough for con-
sumers, and their research laboratory is chasing the goal of 600 Kbps without sacrificing
quality.
This is in the ballpark of broadband-delivery bit rates. The industry is on the verge
of delivering usable full-screen video via a telephone line. This has been a goal of the tele-
com carriers for a very long time, and earlier trials by British Telecom (BT) and Apple were
pointing in this direction as early as the late 1980s.
13.6
Profiles and Levels
The profile and level organization in H.264 is much simpler than in MPEG-4 as a whole
and the way it is defined for part 2. There are only three profiles currently defined:
Baseline
●
Main
●
Extended
●
Within these profiles there are five main levels with some sub-levels also defined. In
total there are 15 discrete levels supported.
The main profile (Level 3) is becoming the focal point of interest for H.264 encoder
manufacturers that work in the broadcast TV industry.
Because H.264, AVC, and MPEG-4 part 10 are all the same codec, the profiles and lev-
els are summarized together in Appendix G.
13.7
Tool Support
No other codec has as many tools as H.264. It is a superset of all the other codecs. You
could develop a setup on another codec and optimize it to get good performance. Then,
you could apply that same setup to H.264 and add the extra tools to gain even better per-
formance than your original codec could possibly manage.
This is a short list of some of the feature enhancements in H.264 over the earlier codecs:
DCT algorithm works at 4
×
4 pixels instead of 8
×
8 but also supports 8
×
8
●
DCT is layered using Hadamard transforms
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Color sampling supported at 4:2:2 and 4:4:4.
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Up to 12 bits per pixel are possible
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Motion compensation blocks are variable sizes
●
Arithmetic variable-length coding
●
Built-in de-blocking filter and hinting mechanism
●
Rate-distortion optimizer
●
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