Image Processing Reference
In-Depth Information
13
The H.264 Codec
13.1
H.264
H.264 is the most recently available codec. It is designed for general-purpose use and is
known by several different names. This is a legacy of the various groups collaborating
during the evolution of their standards and deciding in the end that they should work
together as a single team.
H.264 is important because it incorporates the compression work done by several
different industry bodies into the same standard. Thus, the same codec foundation is used
across a much wider landscape.
H.264 is also known as MPEG-4 part 10. The MPEG-4 standard initially only sup-
ported the part 2 codec. Part 10 was added to include H.264 coding, which is also known
as Advanced Video Coding (AVC).
13.2
Why Do We Need Yet Another Codec?
The H.264 codec is targeted at applications that previously would have used MPEG-2,
H.263, and the earlier MPEG-4 part 2 video codec. It improves on a lot of capabilities that
were available before and makes them more flexible and useful. Elements that were joined
together and fixed are now more loosely coupled. Also, you can control certain aspects
directly that were hardwired internally before. H.264-coded video runs at about half the
bit rate that MPEG-4 part 2 requires. It has the added benefit that the image quality soft-
ens as the compression ratio increases.
13.2.1
Mobile Devices
Although the MPEG-2 codec performed very well at bit rates delivered by a domestic
DVD player, it could not achieve the desired quality at bit rates available to mobile
devices. This was a design goal for H.264. The new H.264 codec was designed to scale
from very low bit rates to high-definition and digital-cinema applications. To do this, more
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