ADS Technologies USBAV-708 INSTANT VIDEOMPX, Руководство пользователя

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The
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New to DivX 5.1 is the Rate-Distortion algorithm, enabled to varying degrees
when the Performance/Quality setting is either Slow or Slowest . The rate-
distortion algorithm allows the outcome of various decisions made by the
encoder to be evaluated intelligently with respect to bit spend against quality gain
where previously simple algorithms would govern the process.
Every decision made as a video is encoded has an impact on both the
rate and
the distortion . The rate is a term used to describe the bits spent, distortion to
describe the change in some measure of quality based upon any particular
decision.
Decisions evaluated by the rate-distortion algorithm might include the coding of
blocks (should they be intra-coded, predicted, or skipped), or which of several
possible motion vectors for a block yields the best balance of bits spent against
quality.
With respect to the illustration opposite,
consider any decision the encoder might
make and imagine three possible
outcomes—A, B and C.
Under normal circumstances the
encoder will make the best possible
choice in terms of quality. In the
illustration this is decision C. However,
the rate-distortion algorithm might
instead choose decision B since it offers
comparable quality at a much lower bit
spend.
Notice that although decision B leads to
marginally lower than optimum quality
for this particular decision, overall
quality will rise because the encoder has
more free bits to spend.
The rate-distortion algorithm evaluates
decisions based upon a rate-distortion
curve, describing the change in
distortion necessary for a rise in bit
spend to be considered a good decision.
The Rate-Distortion algorithm
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Bits
Decision A
Decision B
Decision C
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Bits
Decision A
Decision B
Decision C