Solution for H265 but allows H264
https://superuser.com/questions/995590/h-265-and-opus-in-mp4-container-is-it-possible
# ffmpeg -i test.mp4 -c:a opus -strict -2 -c:v copy opus.mp4
or
-c:v libx264 -preset veryfast -vb 140k -c:a libopus -b:a 12k -vbr on -compression_level 10 -frame_duration 60 -application audio
Solution for H265 but allows H264
https://superuser.com/questions/995590/h-265-and-opus-in-mp4-container-is-it-possible
# ffmpeg -i test.mp4 -c:a opus -strict -2 -c:v copy opus.mp4or
-c:v libx264 -preset veryfast -vb 140k -c:a libopus -b:a 12k -vbr on -compression_level 10 -frame_duration 60 -application audio