https://discuss.kde.org/t/rendering-video-with-multiple-audio-tracks-with-2-languages/16305
How do I render a video with 2 languages, and have a video player like VLC choose between 2 audio tracks (i.e. 1 track for Japanese and the other for English)?
I don't know how to do it with KDE's tools, but on the command line with ffmpeg you can do something like this:
ffmpeg -i video_track.mp4 -i audio_jp.m4a -i audio_en.m4a -map 0:v -map 1:a -map 2:a -metadata:s:a:0 language=jpn -metadata:s:a:1 language=eng -c:v copy -c:a copy output.mp4
Breaking it down, it:
ffmpeg-i flag) -- a video file, and two audio files.-map 0:v maps input 0 (the first file) as video (v) to the output file and -map 1:a maps the next input as audio (a), etc.-metadata:s:a:0 language=jpn sets the first audio track (again counting from 0...) to Japanese; the second metadata option sets the next audio track to English.-c:v copy specifies that the video codec should be copied directly (i.e. don't re-encode -- remove this if you DO need to re-encode)-c:a copy specifies that the audio codec should be copied directly (i.e. don't re-encode -- remove this if you DO need to re-encode)output.mp4 -- finally, list the name of the file you want the result written into.See documentation here: https://ffmpeg.org/ffmpeg.html
If you need another language in the future, I think the language abbreviations are the three letter codes from here: https://en.wikipedia.org/wiki/List_of_ISO_639-2_codes -- but I'm not certain on that.
Not rendering. Muxing, which is short for multiplexing. Lots of software can do this, including MKVToolNix, ffmpeg, and GPAC/MP4Box. If you're also encoding the video, Handbrake could do the job.