Max_P, 16 days ago FFmpeg should be able to do that without reencoding the video, possibly also audio. Basically you want to use -c:v copy -c:a copy and remap the right channel to a single mono channel, and remux all of that in a new output file. trac.ffmpeg.org/wiki/AudioChannelManipulation
FFmpeg should be able to do that without reencoding the video, possibly also audio. Basically you want to use -c:v copy -c:a copy and remap the right channel to a single mono channel, and remux all of that in a new output file.
-c:v copy -c:a copy
trac.ffmpeg.org/wiki/AudioChannelManipulation