Image Processing Reference
In-Depth Information
What Is a Video Compressor?
All video compressors share common characteristics. I will outline them here and by the
end of the topic you should understand what all of these terms mean. In fact, these terms
describe the step-by-step process of compressing video:
Frame difference
Motion estimation
Discrete cosine transformation
Entropy coding
Wow! Right now you may be thinking that this is probably going to be too hard.
Refrain from putting the topic back on the shelf just yet though. Compression is less
complicated than you think. If we take it apart piece by piece and work through it one
item at a time, you will see how easy it is. Soon, you will be saying things like, “I am
going to entropy code the rest of my day,” when what you actually mean is you are
going home early because there is nothing to do this afternoon. You can have a secret
guffaw at your colleagues' expense because you know all about video compression
and they don't.
The Informed Choice Is Yours
Despite all the arguments about the best technology to use, in the end your decisions
may be forced by your marketing department arguing about reaching larger audi-
ences. Those decisions should be backed up by solid research and statistics. On the
other hand, they might be based just on hearsay. The consequences of those decisions
will restrict your choice of codecs to only those that your selected platform supports.
However, you will still have some freedom to innovate in building the production
Video compression is only a small part of the end-to-end process. That process starts
with deciding what to shoot, continues through the editing and composition of the
footage, and usually ends with delivery on some kind of removable media or broadcast
system. In a domestic setting, the end-to-end process might be the capture of analogue
video directly off the air followed by digitization and efficient storage inside a home video
server. This is what a TiVo Personal Video Recorder (PVR) does, and compression is an
essential part of how that product works.
There is usually a lot of setting up involved before you ever compress anything.
Preparing the content first so the compressor produces the best-quality output is very
important. A rule of thumb is that about 90% of the work happens before the
compression actually begins. The content of this topic reflects that rule of thumb:
about 90% of the coverage is about things you need to know in order to utilize
that 10% of the time you will actually spend compressing video in the most effective
way possible.
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