I created a video using Final Cut Pro X (10.1.4) and added a commentary using the voiceover feature. I was surprised to discover that FCPX does not support outputting a file with multiple audio tracks.
I disabled the commentary track and saved the project in 1080p with just the regular audio (main.m4v).
I then re-enabled the commentary and adjusted the regular audio and exported a 720p version with just the commentary track (commentary.m4v).
How do I use ffmpeg to create final.m4v, which would be main.m4v but with the audio track from commentary.m4v as a secondary audio track?
ffmpeg
-only