Image Processing Reference
In-Depth Information
Maintaining high quality at low bit rates requires the encoder to work very hard
indeed and this reduces the chances of processing in real time. Therefore, small bit rate
and high quality are possible, but not if you want the output delivered quickly. This may
be possible if you spend more money on parallelizing the problem across a distributed
architecture. Building grids or render walls is not trivial and certainly is not cheap.
Analog recording systems are cheap but suffer from time-base problems that can
cause the whole frame to arrive early or late. The capture system can usually compensate
for this, but not always. Sometimes the problem is related to the tape, and this is appar-
ent when you experience a syncing problem at the same point in the playback every time.
A more difficult issue to do with time bases is horizontal synchronization. This can
cause each line to be displaced slightly left or right of its correct position. Any vertical
edges then become ragged. This introduces some high-frequency components in the ver-
tical axis, and these are hard to encode. Fixing this problem is very difficult and complex,
so you will often put up with it in order to save sinking a lot of cash into your equip-
ment—hat is, unless quality becomes a dominant factor and you then are able to justify
deploying some heavyweight solution.
Now Set Up Your Codec
Codecs represent the video as a series of macroblocks. Making the encoding lossy at the
macroblock level reduces the bit rate. The encoder expends a lot of effort on the motion
estimation/compensation logic. This reduces the number of macroblocks to be included in
the output stream but it is computationally very expensive.
The H.264 codec is especially compute intensive in this area but is amazingly effi-
cient compared with all the other codecs once the video has been compressed.
Always purchase the professional versions of the encoding tools. They will
generate better-quality results than the limited-edition or basic versions.
If you have the time, set the encoder to do the most thorough job on the compression. It
will take longer, but provided you have not over-promised to your customers, that com-
pression should not take longer than you would have predicted (given some experience,
of course). Switch on 2-pass encoding, variable bit rate, and any additional tools that the
encoder deploys to do a better job.
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