[FFmpeg-devel] [PATCH] mpeg2: remove idct randomisation

Michael Niedermayer michaelni
Mon Jun 21 01:08:20 CEST 2010

On Sun, Jun 20, 2010 at 03:31:00PM -0700, Jason Garrett-Glaser wrote:
> On Sun, Jun 20, 2010 at 3:23 PM, Michael Niedermayer <michaelni at gmx.at> wrote:
> > On Sun, Jun 20, 2010 at 11:21:28PM +0100, Mans Rullgard wrote:
> >> Since the beginning of time, the MPEG2 decoder has XORed the LSB of
> >> all block coeffs into the last one, probably to produce a random
> >> dithering for masking DCT mismatch errors. ?This patch removes this
> >> randomisation. ?As a side-effect, the value of block_last_index is
> >> now correct.
> >
> > This violates the spec
> WHAT?!  The spec mandates this?!  

it was something to reduce numerical differences between different idcts
as the idct is not specified bit exactly.

>Then we should at least fix the
> block_last_index value, which is wrong whenever this mode is used.
> Dark Shikari
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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

If you really think that XML is the answer, then you definitly missunderstood
the question -- Attila Kinali
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