Image Processing Reference
In-Depth Information
How Encoders Work
Now We Are Getting Somewhere
Let's take a look at some of the issues that affect the whole video-compression process.
Then you can make an informed choice about whether to go for speed or cost-effectiveness.
This chapter sets the scene for a trip down memory lane, looking at some long-established
codecs and then moving right up to date with details of the latest models.
Video-Compression Technologies
If you buy a software product such as the Popwire Technology Compression Master,
Sorensen Squeeze, or Discreet Cleaner you can start encoding your video right away. By
using the built-in templates you can begin without knowing anything at all about how the
compression works. It helps to read the manual, of course, but often the quick-start guide
is all you need to begin. Your next level of advancement is to edit the templates.
Eventually you can create your own from scratch.
You are not going to achieve the best possible compression performance without
knowing something about how it works. You don't have to know all the mathematical the-
ories, but an overall appreciation of what is under the hood is a good thing.
I'll explain the mechanics of what compression does and the key concepts involved
in it. I'll use pictures because arcane mathematical formulas are not very helpful unless
you are in the business of implementing a codec. We should all be eternally grateful that
the people at Popwire, Sorensen, Envivio, Apple, Real Networks, Microsoft, Discreet, and
other companies already did that hard work for us.
There are many proprietary codecs available. These are closed systems and the inner
workings are not generally accessible, so our discussions here will mainly be based around
the MPEG standards because they are open and well-known.
A good place to start is with the earliest and simplest, MPEG-1, and then proceed
through the enhancements that MPEG-2 provided, follow that with MPEG-4 part 2, and
finish with the H.264 codec (otherwise known as JVT, AVC , or MPEG-4 part 10). This is
currently the most advanced, standards-based codec available. Some alternative codec
possibilities will be discussed later on.
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