Set MP4 thumbnail

Try to use ffmpeg -disposition option along with -map.

ffmpeg -i video.mp4 -i image.png -map 0 -map 1 -c copy -c:v:1 png -disposition:v:1 attached_pic out.mp4

More information can be found in ffmpeg documentation:

• -map option
• ffmpeg main options

Also, please note, it's not guaranteed that the image you use will be showed in a video preview or as a file tumbanail, because different software programs may not use embedded thumbnails at all.

This can be done with the TagEditor project. To add:

tageditor -s cover=y.jpg --max-padding 125000 -f z.mp4

To remove:

tageditor -s cover= --max-padding 125000 -f z.mp4

Yes you can, but support depends on your container format; mp4 will work but others may not.

ffmpeg -i INPUT.mp4 -i IMAGE.png -acodec copy -vcodec copy -map 0 -map 1:0 OUTPUT.mp4