[Libav-user] AAC with FLV

[Paul B Mahol]

On 4/24/13, Brad O'Hearne <brado at bighillsoftware.com> wrote:
> On Apr 24, 2013, at 5:05 AM, Pradeep Karosiya <praks411 at gmail.com> wrote:
>
>> Hi Brad,
>>
>> Have you found the solution to your issueof audio distortion. I'm also
>> facing a similar issue while encoding with AAC and this is happening for
>> same audio parameters sample rate: 44100, sample format:
>> AV_SAMPLE_FMT_FLTP
>> and number of channels = 2. For mono it is working fine. So I guess the
>> problem could be with planar data. Please let share with me.
>
> Pradeep -- thanks so much for your reply! Given the hair-pulling (what
> little I have of it to pull) required thus far with this problem, it is
> encouraging to know there's someone else to validate the difficulties I am
> experiencing (so I have a fighting chance of still being semi-sane!)
>
> To answer your question, no, I have not figured this out yet. As you may
> have gathered from my posts on this topic, I have taken a working codebase
> and simply changed the destination sample format for resampling (from
> AV_SAMPLE_FMT_S16 to AV_SAMPLE_FMT_FLTP) and the codec in play (ADPCM_SWF to
> AAC), and audio went from perfect to garbage. That garbage became
> understandable audio with distortion simply by changing the destination
> sample rate from 44100 (which is the same as the source sample rate) to
> 96000, which is completely confusing to me.
>
> Another poster astutely recommended to reexamine all assumptions and
> understand that the changes above constitute a "different situation", but in
> acknowledging that, it is important to note what is *not* different: the
> entire handling pipeline. There is absolutely zero data byte value
> manipulation taking place in my code -- I am merely feeding data I have to
> FFmpeg data / array filling, resampling, and encoding functions. The parts
> I'm changing are merely settings, which leads me to two possibilities I'm
> testing at this point:
>
> 1. My code (specifically data array pointers on the captured samples) wasn't
> right to begin with, which would seem a little strange, given that it was
> producing perfect video / audio encoding with other settings / codec. If I
> had passed bad pointers or array structure / layout / population I would
> have expected any format to blow up.
>
> 2. There is some issue in FFmpeg -- and you are right, the glaring
> difference in use case here was going from a non-planar destination to a
> planar destination. This was even more confusing for me, because my captured
> format was planar -- so as a test I skipped resampling entirely and passed
> the encoder my source data array (which should have been in the exact format
> as the destination array once resampled), and it blew up. I do believe
> there's an issue that revolves around the fact the destination format is
> planar. I mean, my original stab at this resampled from a source array with
> the same channel layout, sample format, and sample rate as the destination
> -- the encoder can take the destination fine, but blows up if I pass it the
> source (again, should be no different from the resampled destination) -- how
> weird is that?  This would seem to be a fair indication that, to quote the
> Princess Bride movie, "I do not think it means what you think it means",
> with respect to the sourc
>  e data array. But it sure seems weird that if I were handling the source
> data array improperly, that it wouldn't have blown up before and that I'd be
> able to get perfect audio from it using another sample format...so I'm still
> allowing for the possibility that swr_convert doesn't like source and
> destination with identical sample formats for some reason.
>
> I'll keep you posted. One other thing I've been looking into are the "align"
> parameters on a number of these functions. They aren't documented very well,
> and there appears to be more than one way to interpret alignment and the
> parameter values, so if someone could expound on that further, I'd
> appreciate it.


Stop this nonsense trollfest. There is no bug in ffmpeg.

Planare sample format store each channel samples in separate buffer.
You can not access them with single pointer.

>
> Thanks,
>
> Brad
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