[FFmpeg-user] 'showspectrumpic' filter: scaling of the frequency axis and fft windows size

Paul B Mahol onemda at gmail.com
Fri Sep 13 17:01:22 EEST 2019

On 9/13/19, Wolfgang Hugemann <auto at hugemann.de> wrote:
> Today, I have been experimenting with the 'showspectrum' filter, mostly
> with 'showspectrumpic'.
> I think there is a bug in the log scaling of the frequency axis if (and
> only if) it doesn't start at zero: The ratios of the frequency axis'
> labelings is not constant, they grow with larger values.
> I had a quick look at the source code and gained the impression that the
> fft windows size is based on the height of video created (?). At least
> it cannot by specified in the filter options.

Because used fft accepts only power of 2 sizes.
There is code already for more advanced fft but it is not optimized,
and thus not yet used.

> Kind regards
> Wolfgang Hugemann
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