[FFmpeg-user] down sampling

Paul B Mahol onemda at gmail.com
Sun Dec 30 14:20:49 EET 2018

On 12/30/18, Michael Koch <astroelectronic at t-online.de> wrote:
> Am 28.12.2018 um 11:46 schrieb Paul B Mahol:
>> One can now use afftfilt to shift frequencies around in frequency domain.
>> It should be easier than using amultiply filter.
> c:\ffmpeg\ffmpeg -f dshow -channels 2 -i audio="Mikrofon (Realtek High
> Definiti" -af
> volume=30,afftfilt='real=real(b+300,ch)':'imag=imag(b+300,ch)' -f nut -
> | c:\\ffmpeg\ffplay -
> I've just tested this and it works fine. There is no error message when
> (b+300) becomes larger than the available number of bins. How does
> afftfilt handle this case?
> Does real(too_large_number,ch) return zero?

No, it clips and return value in max bin.
If you want explicit zero you will need to change your expression.

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