Thumbnail | cover
March 5, 2022
12:53 PM
To add an embedded cover/thumbnail:
ffmpeg -i [file] -i IMAGE -map 0 -map 1 -c copy -c:v:1 png -disposition:v:1 attached_pic [file]

Not all muxers support embedded thumbnails, and those who do, only support a few formats, like JPEG or PNG.
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