[FFmpeg-devel] ffvorbis, inverted output

Robert Swain robert.swain
Sun Sep 28 18:16:24 CEST 2008


2008/9/28 Michael Niedermayer <michaelni at gmx.at>:
> On Sun, Sep 28, 2008 at 03:17:29PM +0100, Robert Swain wrote:
>> 2008/9/28 Michael Niedermayer <michaelni at gmx.at>:
>> > 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
>>
>> Just 03_vorbis_vwin_tables_align.diff or all? I guess you meant just 03.
>
> i meant just 03 here, yes

Committed.

Rob




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