I've tried combining different files on multiple occasions (e.g. add extra audio streams in different languages to a video, so that you can select your audio stream/language) but it never worked. That is, when playing the resulting mkv with VLC Media Player, all the non-default audio streams are silent. VLC also allows you to select video streams, so I tried combining two of those, but whichever is not set as default is "empty" (doesn't play). When I probe the file, all streams are there though, and containing bytes.
I try something like this:
ffmpeg -i "one.mkv" -i "two.mkv" -map 1 -map 0 -c copy "result.mkv"
I've tried combining video with pure audio files (extracted from a translated video), I've tried re-encoding everything, but nothing works. What is the secret? What can go wrong with this simple command? Is it something to do with frame rate or whatever the equivalent is for audio, I don't know. On another occasion, the sound became choppy after combining.
