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

[Paul B Mahol]

On 4/22/19, Nicolas George <george at nsup.org> wrote:
> Paul B Mahol (12019-04-21):
>> https://dspguru.com/dsp/faqs/multirate/resampling/
>>
>> 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.
>
> Resampling MAY involve interpolation, to enhance the subjective quality
> of the output.

It is not MAY, it MUST involve interpolation in almost any scenario.

>
>> If you haven't noticed, this is just upsampling/downsampling without
>> lowpass.
>> And that is not resampling in any way.
>
> No matter how many times you repeat it, saying that changing the sample
> rate is not resampling will not make it true.

By your flawed reasoning asetrate filter is doing resamping too.

>
>> That is just your opinion now, you need to provide technical terms
>> to support your statements.
>
> I have given technical considerations: we have automatic sample rate
> negotiation. These filter would not fit with it.

If you haven't tried them, they fit well with sample rate negotiation.
Filters change sample rate metadata by integer factor up or down.

>
> What have you provided besides your opinion and links to generic
> considerations that do not substantiate your views?

I have provided actual facts, and not opinions unlike you.

>
>> Another option to aresample filter would just confuse users.
>
> Less so than yet another pair of filters that do almost exactly the same
> thing as others.

No filter in libavfilter does what those filters do.

And there is reason why SoX have those as separate filters and not some
strange combination with their generic resampling effect.