Replace audio stream from one file with audio stream from another

Question

I have got two video files: .mp4, with a single (incorrect) audiostream, and an .mkv, with two audio streams (one incorrect, the other correct)

Is there a way to replace the audio of the .mp4 file with the second stream in the .mkv?

Thanks

Answer 1

You'd need to extract the audio from the MKV first and then combine remux the MP4 with the new track. Something like this should work:

ffmpeg -i vid.mkv -acodec copy -vn audio.ext
ffmpeg -i vid.mp4 -i audio.ext -vcodec copy -acodec copy -map 0:1 -map 1:0 final.mp4