[FFmpeg-devel] Error in ATRAC1 decoder?

[Даниил Чередник]

Thank you for answer.

If I understood available ATRAC1 docs, the purpose of this delay line is
just to compensate delay of 1st QMF because for 1st and 2nd band we have
two QMF but for 3rd band just one.

About test, yes for some reason this patch brakes it. I will try to find
out. Sorry, I should have done it before.

I tried to decode "The Four Seasons, Concerto Alla Rustica in G - Winter-
Largo.aea" sample, the results are:
without patch: https://yadi.sk/i/PCFplrafkWEFC
with patch: https://yadi.sk/i/iLUR188gkWEFn
On zoomed spectrogram it is possible to find aliasing if decode without
patch. I can share decoded wav file if needed.



On Mon, Nov 16, 2015 at 3:45 AM, Michael Niedermayer <michael at niedermayer.cc
> wrote:

> On Sat, Nov 14, 2015 at 02:59:30AM +0300, Даниил Чередник wrote:
> > Hello!
> >
> > I have noticed if decode
> >
> https://samples.ffmpeg.org/A-codecs/ATRAC1/Test%20tones%20disc%20-%20Chirp.aea
> > file by ffmpeg we got aliasing near 11025Hz. Screenshots:
> > https://yadi.sk/i/r-95jZkKkSnbu https://yadi.sk/i/PV92LNESkSnby
> >
> > I was tried to solve it:
> >
> > ATRAC1 - hybrid codec, has two stacked QMF and splits the signal into 3
> > band before MDCT. Thereby we need to compensate delay of one QMF to
> > achieve reconstruction.
> > There is a delay line but it looks like delay for 23 sample is not
> correct.
> > I have done some experiments and got 39 should be right delay. Results of
> > decoding with patch: https://yadi.sk/i/yooaIQrmkSncB
> > https://yadi.sk/i/CUXsH7-CkSncK
> >
>
> > To be honest I am not a prof in math and it would be great if someone
> > recheck it from math perspective.
>
> i dont think math can help here
> whatever a format requires that has to be done, this could even be
> wrong from a math point of view of a ideal transform
>
>
> >
> > There is a patch in attach.
>
> the patch also affects the atrac1 fate test
> have you checked if the new output for that test is better than the
> old ?
>
> make V=2 fate-atrac1
>
> also have you looked at other files, is this improving all files ?
> any that get worse ?
>
>
> [...]
>
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> Many that live deserve death. And some that die deserve life. Can you give
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>
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-- 
Daniil Cherednik