[Libav-user] Audio quality loss while encoding

Paul B Mahol onemda at gmail.com
Thu Apr 25 01:54:23 CEST 2013

On 4/24/13, Brad O'Hearne <brado at bighillsoftware.com> wrote:
> On Apr 24, 2013, at 11:04 AM, Alex Cohn <alexcohn at netvision.net.il> wrote:
>> And to set
>> data[1]=data[0] + plane_size;
>> is most likely not enough because both data[0] and data[1] must be
>> aligned.
> Hey Alex, thx for the reply. You hit one of the magic words ("aligned") that
> I'm investigating further. I've seen "align" as a parameter in a number of
> the avcodec function calls, and there doesn't appear to be much discussion
> regarding the proper setting of this value (like for example "0 = default"
> -- which doesn't explain what the "default" actually means). Also understand
> that alignment even in audio samples has other interpretations, so I'm
> trying to make sure I'm not reading something into what FFmpeg means by
> this.
> So back to your statement that "both data[0] and data[1] must be aligned".
> What specifically do you mean by this?

You call av_samples_alloc_array_and_samples() with align set to 0, which means
channel data planes are aligned along 32 byte boundary. Is this really the case?

Set align argument to 1 if to make them aligned along 1 byte boundary.

> Thanks,
> Brad
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