[FFmpeg-cvslog] r18860 - in trunk/libavcodec: ac3dec.c ac3dec_data.c ac3dec_data.h eac3dec.c

[Michael Niedermayer]

On Fri, May 22, 2009 at 10:38:41PM -0400, Justin Ruggles wrote:
> Michael Niedermayer wrote:
> > On Wed, May 20, 2009 at 09:21:11PM -0400, Justin Ruggles wrote:
> >> Michael Niedermayer wrote:
> >>> On Tue, May 19, 2009 at 10:13:34PM -0400, Justin Ruggles wrote:
> >>>> Michael Niedermayer wrote:
> >>>>> On Tue, May 19, 2009 at 06:23:38PM -0400, Justin Ruggles wrote:
> >>>>>> Michael Niedermayer wrote:
> >>>>>>> On Sun, May 17, 2009 at 08:53:27AM +0200, jbr wrote:
> >>>>>>>> Author: jbr
> >>>>>>>> Date: Sun May 17 08:53:24 2009
> >>>>>>>> New Revision: 18860
> >>>>>>>>
> >>>>>>>> Log:
> >>>>>>>> eac3dec: use 16-bit pre-mantissas instead of 24-bit in AHT decoding. it is
> >>>>>>>> simpler and also fixes a bug in GAQ dequantization.
> >>>>>>> are you sure 16bit precission is enough for that?
> >>>>>>> what effect does this compared to double precission floats have on the
> >>>>>>> PSNR ?
> >>>>>> stddev:    7.95 PSNR: 78.30 bytes:  3999744/  3999744
> >>>>> and what is that?
> >>>>>
> >>>>> we have raw -> encoder -> ac3 -> double fp decoder -> raw2
> >>>>>                               -> 16bit     decoder -> raw3
> >>>>>
> >>>>> PSNR of raw2 - raw vs. PSNR raw3 - raw is what we care about.
> >>>>> That would make 2 PSNR scores though, a before and a after
> >>>>>
> >>>>> the second part we care about is the difference to a reference decoder
> >>>>> that should mention which reference decoder is used though
> >>>> I can't compare to raw in this case because I don't have access to a
> >>>> professional E-AC-3 encoder which uses the AHT quantization.  But I can
> >>>> compare to decoded output from Nero's E-AC-3 decoder.
> >>>>
> >>>> nero vs. ffac3 svn
> >>>> stddev:  131.16 PSNR: 53.96 bytes:  3998716/  3999744
> >>> why does the output differ so much to begin with?
> >> That I'm really not sure of.  I don't have access to the Nero decoder
> >> other than begging madshi to decode samples for me like I did in this case.
> > 
> > isnt there some official reference decoder like with ISO/ITU standards?
> 
> Dolby Media Decoder. List price: $1900

i see

i guess as a compromise we could use double precission code of our decoder
as reference and make any fixed point optims be very close in terms of
output to that.

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

Asymptotically faster algorithms should always be preferred if you have
asymptotical amounts of data
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 189 bytes
Desc: Digital signature
URL: <http://lists.mplayerhq.hu/pipermail/ffmpeg-cvslog/attachments/20090523/67a96490/attachment.pgp>