[FFmpeg-devel] [PATCH 2/3] avfilter: add audio upsample filter

Paul B Mahol onemda at gmail.com
Sun Apr 21 13:26:20 EEST 2019

On 4/21/19, Nicolas George <george at nsup.org> wrote:
> I apperciate the efforts to reply more than half a line.
> Paul B Mahol (12019-04-21):
>> It is not kind of resampling. Resampling is specific and belongs to
>> separate library.
> There is no doubt it IS a kind of resampling: it is in the name. The
> question is whether is it specific enough to warrant a separate
> interface.


Resampling involves interpolation.
If I do resampling with aresample and resampling with factor 2 from
44100 to 88200
I can see there is still some spectrum data in highest frequencies.

>> The oversampling is another thing, and doing only upsampling/downsampling
>> via libswresample is fragile/incomplete, as you need some kind of
>> lowpass.
>> (be it IIR, FIR or simple FFT) after upsample and before downsample.
> There are various way of doing a resampling with various properties.
> This is just another one.

If you haven't noticed, this is just upsampling/downsampling without lowpass.
And that is not resampling in any way.

>> That is why it best fit into lavfi because it is just one block of
>> processing with multiple solutions.
> Making it a separate filter is the easy solution, but not the good one.
> It is reporting all the choices to later or the end user. That makes for
> easy quick code now, but terrible use later.

That is just your opinion now, you need to provide technical terms
to support your statements.

>> Also how that could be exported? It does not belong there.
> Options. We already have them, just add a few. And in that case, it
> becomes accessible for all filters.

Another option to aresample filter would just confuse users. Two options
which would set rate with completely different outcome.

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