[FFmpeg-devel] [PATCH] remove out-dated ADPCM frame_size handling in libavformat

[Michael Niedermayer]

On Sat, Sep 11, 2010 at 11:30:07AM -0400, Justin Ruggles wrote:
> Michael Niedermayer wrote:
> 
> > On Wed, Sep 08, 2010 at 06:49:36PM -0400, Justin Ruggles wrote:
> >> Justin Ruggles wrote:
> >>
> >>> Michael Niedermayer wrote:
> >>>
> >>>> On Mon, Sep 06, 2010 at 08:11:38AM -0400, Justin Ruggles wrote:
> >>>> [...]
> >>>>> Index: tests/ref/acodec/g726
> >>>>> ===================================================================
> >>>>> --- tests/ref/acodec/g726	(revision 25042)
> >>>>> +++ tests/ref/acodec/g726	(working copy)
> >>>>> @@ -1,4 +1,4 @@
> >>>>> -5d8cce28f83dd33c3c7eaf43a5db5294 *./tests/data/acodec/g726.wav
> >>>>> -24082 ./tests/data/acodec/g726.wav
> >>>>> -4f1ba1af75dee64625a1c852e6cd01d3 *./tests/data/g726.acodec.out.wav
> >>>>> -stddev: 8504.69 PSNR: 17.74 MAXDIFF:31645 bytes:    96104/  1058400
> >>>>> +fd090ddf05cc3401cc75c4a5ace1d05a *./tests/data/acodec/g726.wav
> >>>>> +24052 ./tests/data/acodec/g726.wav
> >>>>> +74abea06027375111eeac1b2f8c7d3af *./tests/data/g726.acodec.out.wav
> >>>>> +stddev: 8554.55 PSNR: 17.69 MAXDIFF:29353 bytes:    95984/  1058400
> >>>> the number of samples encoded seems to be changing and not equal to
> >>>> the input
> >>> When the frame size in the encoder makes frames end on a byte boundary
> >>> without any padding, the output is always identical.  Since codes are
> >>> between 2 and 5 bits long, how would the decoder distinguish between
> >>> padding to a byte boundary and another valid code?  I'll double-check,
> >>> but it seems that the decoder currently treats padding as additional
> >>> samples.
> >> I've confirmed that this is the cause of the difference.  The parameters
> >> used by the regression test give a 4-bit code size.  When the frame size
> >> is odd, that leads to 1 extra sample being decoded by the decoder
> >> because of padding.  In the current version, because of resampling from
> >> 44100 Hz to 8000 Hz, the frame size actually varies from frame-to-frame.
> >>
> >> Current:
> >> source samples             = 264600
> >> resampled samples          =  47991
> >> number of odd-sized frames =     61
> >> decoded samples            =  48052
> >> decoded data bytes         =  96104
> >>
> >> Patched:
> >> source samples             = 264600
> >> resampled samples          =  47991
> >> number of odd-sized frames =      1 (the last frame)
> >> decoded samples            =  47992
> >> decoded data bytes         =  95984
> >>
> >> So choosing a frame size that forces the encoder to only use padding for
> >> the last frame (which this patch does) seems to be the appropriate thing
> >> to do.
> > 
> > the patch is ok then
> > the regression test still is completely broken though because it does not
> > seem to compare files of equal sampling rate if my guess is correctly
> 
> Would it be better to resample back to 2-channel 44100 Hz during
> decoding

imho yes


> or to create another reference that is 1-channel 8kHz?  The
> same situation applies for the pcm_s24daud test, which is 6-channel 96kHz.
> 
> -Justin
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-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Breaking DRM is a little like attempting to break through a door even
though the window is wide open and the only thing in the house is a bunch
of things you dont want and which you would get tomorrow for free anyway
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