How to convert an mp4 to mp4 using FFmpeg?
I figured one way that works (not sure if it is optimal). Running
ffmpeg -i broken.mp4 -pix_fmt yuv420p -crf 18 good.mp4
Creates an MP4 that is a bit larger (probably minimally worse in terms of quality) ... and that works on my TV set.
(but I am still looking for other answers, if there are any)
Use the following options:
-c:v libx264 -crf 24 -pix_fmt yuv420p -tune film -c:a aac -b:a 192k -ar 44100 -vol 300 -strict -2 -speed fastest
The final result should run smoothly on most TVs.