[FFmpeg-devel] ffvorbis, inverted output

[Michael Niedermayer]

On Sun, Sep 28, 2008 at 03:00:39AM +0300, Siarhei Siamashka wrote:
> On Saturday 27 September 2008, Siarhei Siamashka wrote:
> > On Sunday 14 September 2008, Michael Niedermayer wrote:
> > > On Sun, Sep 14, 2008 at 04:50:59AM +0300, Siarhei Siamashka wrote:
> > > > Hi,
> > > >
> > > > I tried to do PSNR comparison of libvorbis/ffvorbis/tremor and noticed
> > > > that output from ffvorbis is actually inverted (ex. output 0xFFFF in
> > > > libvorbis corresponds to 0x0001 in ffvorbis and so on) when compared to
> > > > the output from the other decoders.
> > > >
> > > > Should this be fixed?
> > >
> > > yes, if all (/most) other vorbis decoders match and we differ from that
> >
> > Can these two patches be used as a fix? The first one adds support for
> > scaled imdct output. The second one inverts output of the decoder (to match
> > libvorbis and tremor) using negative scale factor.
> >
> > As additional bonus, 'copy_normalize' function from vorbis decoder is
> > simplified. Though I get some inconsistent benchmark results (performance
> > difference is negligible with one or another variant getting ahead
> > randomly) and would like someone to confirm that there is no performance
> > regression.
> >
> > Getting scaled imdct output involves sqrt operation and scale factor uses
> > odd power of two, so there is some difference in PSNR compared to SVN
> > trunk (taking inversion into account):
> >
> > stddev:    0.02 PSNR:127.97 bytes: 22057216/ 22057216
> 

> Oops, an extra patch to ensure tables alignment is also needed. It is
> attached.

patch ok

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Those who are too smart to engage in politics are punished by being
governed by those who are dumber. -- Plato 
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