[FFmpeg-devel] [PATCH] [Issue 632] AAC: Decode TNS order zero properly from the bitstream

Michael Niedermayer michaelni
Fri Sep 12 15:33:00 CEST 2008

On Fri, Sep 12, 2008 at 11:06:29AM +0100, Robert Swain wrote:
> Hello,
> 2008/9/12 Alex Converse <alex.converse at gmail.com>:
> > As per tns_data() from the spec, direction and coef_compression are
> > not coded if order == 0.
> Yes, looks fine and correct to me. Michael - do you want me to request
> your OK for such patches or would you prefer I just apply them if I
> think they're OK?

you are maintainer of the code so of course can you apply something if
you think its ok

> > Even after this, something is still wrong with al04_44 (Issue 632) as
> > we are only getting 8 bits of conformance.
> It may be useful to analyse where in the stream the significant
> differences occur in case it's a few isolated cases spread across the
> file. I used this technique previously with success. Basically I
> printed out the channel element types for each channel, found the
> position of the difference in terms of samples (I used `cmp -l` and
> calculated from that bearing in mind that the first AAC frame does not
> get output, but whatever suits you), and then look at the code and the
> tools used for that channel element to figure out where it's going
> wrong.

Its also possible to hack both the reference decoder (or some other
FOSS decoder) and ffmpeg by disabling a specific feature like TNS.
and then compare how different the output is. If the difference stays
its likely not TNS if the difference gets smaller it likely is TNS.
this method can then be used with one tool at a time until the
problem is found.
Its not exactly quick but should have a low failure rate and should be
able to cut down the amount of code which has to be looked through for
the issue

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

No snowflake in an avalanche ever feels responsible. -- Voltaire
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