Automatically select another thumbnail position if it's not valuable

Sometimes, generated thumbnail for a video is just a black image.

Could it be possible to test the image to see if it's, maybe something like, 90% black ? (or 90% mono-color ?) And try some next key-frame to have a better thumbnail ?

See the 2 videos below (VOB_Dolby_Canyon and Webm_testclip)

Edited Sep 27, 2019 by Hugo Beauzée-Luyssen

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