[FFmpeg-devel] Error in ATRAC1 decoder?

[Michael Niedermayer]

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 ?


[...]

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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Many that live deserve death. And some that die deserve life. Can you give
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