[FFmpeg-devel] [PATCH] Apple RPZA encoder

Jason Garrett-Glaser darkshikari
Thu Apr 16 15:23:28 CEST 2009

> I took some time off to wade through that doc. From what I understand,
> I'll need a metric to represent the distortion and output rate.
> Assuming I use a simple variant like least squares or sum of absolute
> differences or whatever, I still don't understand how I can visualize
> and RD curve for this (rpza) case. Do I fix the output size and
> iterate over possible values for the lagrangian parameter to minimize
> the bit cost? If I do that, I still don't quite get how I can
> correlate that bit cost to rpza block coding. Any insights appreciated
> :)

RD = Lambda * Bits + Distortion

For any given lambda, there is an optimal RD score.

Thus, there are two (simple) ways to encode:

1.  Constant lambda; keep lambda the same everywhere, get some target
bitrate as a result.  Effectively constant quality.
2.  Constant bitrate; adjust lambda to get a target bitrate.

In MPEG-like formats, lambda is usually chosen as a per-quantizer
constant.  The exact mapping of lambda to quantizer is usually
determined experimentally.

Dark Shikari

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