[FFmpeg-devel] hardware aided video decoding

Michael Niedermayer michaelni
Sun Jul 8 13:36:23 CEST 2007


On Sun, Jul 08, 2007 at 12:40:31PM +0200, Attila Kinali wrote:
> On Fri, 6 Jul 2007 16:00:58 +0200
> Michael Niedermayer <michaelni at gmx.at> wrote:
> > you can do MC on the card and let the cpu do the idct, note there are 2
> > cases here
> > 1. intra (fits in 8bit)      (simply overwrite whats in the buffer)
> > 2. inter (needs signed 16bit)(add to current data and clip)
> Do you mean here the vectors?

no, i mean the idct output, which can be fitted in 8x8 8bit values for intra
(its just the 8bit samples you will see in the block) but for inter the idct
output is the difference of the prediction (some block from the last frame for
example) and that can differ by +-255 of what you will see so it does
not always fit in 8bit
it would be width*height*2 bytes to transfer in worst case, of course
not all blocks have non zero coefficients so if not much changes in
a frame than many of the blocks will be all 0 after idct, transfering these
would be silly as well as transfering 16bit values for each sample if all
fit in signed 8bit and IMO inter residuals which dont fit in signed 8bit
will be very rare in normal videos, most encoders should rather choose
intra blocks ...


Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Republics decline into democracies and democracies degenerate into
despotisms. -- Aristotle
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