How to add a audio track to a remux without touching the video?

[TheMKVMaker]

Say I only wanted to add a audio track that my TV can decipher (i.e., DTS HD to E-AC3).... how would I go about doing this?

At this point in time handbrake is great for cutting movies down in terms of file size and adding audio tracks as I see fit, but I don't see anyway to only alter the audio tracks - or to be more specific, to add an audio track.

Does anybody here have any experience with doing this?

[Woodstock]

The big issue would be making sure the audio was "in sync" with the video, but you can combine the audio with the MKV using ffmpeg.

I've also used mkvmerge for adding tracks to MKV files, but that's less flexible than ffmpeg. I've only done it when the tracks were from similar sources, like combining a Bluray video with DVD audio/subtitle tracks.

[Radiocomms237]

I do this all the time for DTS Express audio tracks as none of my players will play them.

I use a program called Pazera Free Audio Extractor (URL here) and can't recommend it highly enough.

You may need to extract the audio track(s) from the mkv file first, but if it's just the one default track then you can simply drag 'n drop the mkv file into Pazera, setup the output parameters and "Convert", it will create a new audio file in the source folder.

Then simply mux the new audio track into the existing mkv file with MKVToolNix, setting it as the default, and you're done! (Note that I always leave the original audio track in there as well, for posterity, just no longer set as the default track.)

[maretedkatiegrace]

Have you actually used this program to do this to merge back into 2 hour movies?
Any software that does not add the track live as a remux and that creates a totally independent audio track will have synch issues in the last 1/2 hour of your movie.

[Radiocomms237]

The audio convertor doesn't actually remux the audio back in, I use MKVToolNix to add the track back into the .mkv file, but to be honest, I haven't physically checked for sync issues all the way though the playback.

I only really do this for DTS Express audio tracks, which are typically for the Picture-In-Picture Behind-The-Scenes/Commentary that pops up intermittently throughout the movie, so it's probably not so important as it would be for a main audio track, although may still be annoying if the out-of-sync is bad enough.

P.S. I've also had that happen with a video editing suite, where each time you "split" the file for any reason, it seems to add a slight delay to the audio sync. You may not even notice it unless you've made a lot of edits.