Feat: Sound file preview with sound spectrum (ffmpeg ?)

[inkhey]

Feature description and goals

Making preview for sound is complicated, one way to represent sound into image is spectrum.
There are many software able to generate spectrum from sound.
I do suggest to use ffmpeg showspectrumpic to do so, as it permit to not require a new dependencies, and as ffmpeg is
a good software with good support.

External links:

• https://superuser.com/questions/294154/making-sound-spectrum-images-from-command-line
• https://ffmpeg.org/ffmpeg-filters.html#showspectrumpic