`showcqt’ with basefreq, and endfreq (crop between A0 and C8)

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doc

https://ffmpeg.org/ffmpeg-filters.html#showcqt

#! /bin/sh
ifn="Air on the G String (from Orchestral Suite no. 3, BWV 1068).mp3"
ifnb="`basename \"${ifn}\" .mp3`"
pref="`basename $0 .sh`"

# cqt   -> E0 - D#10
# "myaxis.png": 1920x120 (A0 - C8)
#
# basefreq=27.500
# endfreq=4186.009
# axisfile=myaxis.png
ffmpeg -y -i "${ifn}" -i "myaxis.png" \
    -filter_complex "
[0:a]showcqt=s=1920x1080
,crop=1392:1080:88:0,scale=1920:540,setsar=1[b];
[0:a]showcqt=s=1920x1080:basefreq=27.500:endfreq=4186.009
,scale=1920:540,setsar=1,split[t0][t1];
[1:v]loop=loop=-1:size=2,pad=1920:540:0:(oh-ih)/2[ax];
[t0][ax]blend=all_mode=average[t2];
[t2][t1]blend=all_mode=average[t];
[t][b]vstack[v]
" -map '[v]' -map '0:a' -c:a copy \
  -shortest "${pref}_${ifnb}.mp4"

• If you give “basefreq”, and “endfreq” to showcqt, showcqt wouldn’t render the axis (in most cases). Actually, you can use ‘axisfile’ option, but I’m trying it with “blend” manually.

• “myaxis.png” was made by mk_piano_image.py.