[FFmpeg-devel] [PATCH] H.264 predictive lossless: again

Jason Garrett-Glaser darkshikari
Sat Nov 29 12:58:05 CET 2008

> i cannot see any sense in this change, nor in the similar ones for other
> block sizes. It should be well possible to leave the prediction alone
> add the residual and modify the result in the special cases

I'll deal with the trivial points later; this appears to be the main
substantive issue here.

The easiest, fastest, and least-code way to do predictive lossless is
as follows:

Zero fdec
Add residual to fdec, *without saturation*, so negative numbers get
stored as wrapped-around positive values/etc.  This works because the
standard specifies that overflow shall not occur with
transform_bypass, and so saturation never has to be handled with real
Do prediction

Are you saying that we should instead make a new residual_add function
that *sets* the pixel values equal to the residual instead of
*adding*, so that zero isn't necessary?

Dark Shikari

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