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

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. Kind regards Wolfgang Hugemann