Extract individual audio stems from MKV file?

Well MKVtoolnix will extract the ac3 track from an mkv file.

Then if you have a windows machine you can use:-
BeSweet or
eac3to or
HeadAC3he to convert ac3 to 6 mono waves.

On the Mac side of things the only thing I could find is the 3rd post of this thread on the Mac OSX Audio forum that talks about using Audacity to convert ac3 to 6 mono waves and there's a Mac version of Audacity.

http://www.macosxaudio.com/forums/viewtopic.php?t=33085
Audacity

This is all I could find, hope it helps.

OK, I've just done a test and Audacity works perfectly under Windows, so there's no reason the Mac version shouldn't also work.

1. Install Audacity 1.3.13.

2. Install the FFmpeg import/export library, from the Audacity site. This will allow you to import/export AC3 files.

Now you can open your mkv/mp4 files directly in Audacity and select the AC3 track, but for some reason it downmixes it to stereo So.....

3. Extract your AC3 track from your movie file.

4. Run Audacity and goto Edit->Preferences, this box will popup:-



5. Goto the Import/Export page and under the "When exporting tracks to an audio file" section select "Use custom mix", if you don't do this when you export your file all the tracks will be mixed into one file.

6. Goto File->Open and load your AC3 file, it should load as 6 mono tracks:-



7. Goto File->Export Multiple.

8. Select the export format and location then press Export.

9. You'll get an edit metadata page for each of the 6 tracks just press ok on each.

10. Mission accomplished

Just a quick side note, Audacity doesn't label the 6 mono audio tracks but the ordering is as follows:-

Track 1 = Left front
Track 2 = Right front
Track 3 = Center
Track 4 = LFE(Sub)
Track 5 = Left Surround
Track 6 = Right Surround

No problem, glad to hear you've got it working.

Yep, just tried it and it seems to work with DTS-HD 7.1, heres what I did:-

1. Convert a Blu-ray to mkv using MakeMKV, selecting only the DTS-HD 7.1 track to make it easier.
2. Use MKVExtract from MKVToolsnix to extract the 7.1 audio to a file that has a .dts extension.
3. Load the .dts file into Audacity just like in the 5.1 AC3 example.
4. Export the same as before.