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

Paul B Mahol onemda at gmail.com
Sun Apr 21 12:53:18 EEST 2019

On 4/21/19, Nicolas George <george at nsup.org> wrote:
> Paul B Mahol (12019-04-19):
>> Generic resampling via aresample is completely another filtering that
>> have
>> nothing to do with this filters, for more info read:
>> https://www.oblique-audio.com/technique/oversampling
> Quite the opposite: this page makes it rather clear that oversampling is
> a kind of resampling, with specific settings to ensure particular
> properties of the spectrum.

It is not kind of resampling. Resampling is specific and belongs to
separate library.
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.
That is why it best fit into lavfi because it is just one block of
processing with
multiple solutions. And not one way do it all solution, set once and
forget what it does.

> As such, it should go into the generic resampling filter (or even
> library), enabled by options. That way, it is available not only
> explicitly from expert users but also automatically, when filters
> declare specific samples rates.

Does not make sense to provide this into libswresample library.
Also how that could be exported? It does not belong there.
It would just confuse users, more because it supports only
integer factor multiplication/divide of rates.

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