[FFmpeg-devel] [PATCH] avfilter: add apitch filter

[Paul B Mahol]

On 5/12/19, Michael Niedermayer <michael at niedermayer.cc> wrote:
> On Sun, May 12, 2019 at 11:00:51PM +0200, Nicolas George wrote:
>> Marton Balint (12019-05-12):
>> > Yeah, you are right, what I had in mind was this:
>> >
>> > apitch  ===  asetrate,aresample,atempo
>>
>> Exactly. And reciprocally, atempo = apitch+asetrate+aresample.
>>
>> Furthermore, since it works with the spectrum, the filter that does the
>> hard work can probably easily output at any sample rate, at a cost much
>> lower than resampling afterwards. Therefore, it makes most sense to have
>> a single filter with all three parameters (sample rate, speed adjustment
>> and pitch adjustment).
>
> and if thats done in our resampler than that can also be combined with
> changing the channel order, layout, sample type and so on.
> Iam not sure its a good idea but purely technically it should be more
> efficient to do it all together.
> Also swresample already supports an external FFT resampler so it might
> actually fit in there nicely and it might even allow us to remove an
> external
> dependancy without loosing a feature. (assuming the new FFT resampler
> would be equally good)
>
>

To make it work dynamically, filter must resample audio internally.