There haven’t been many easy options for editing 5.1 AC3/DTS audio streams with paid or free programs. Even renaming the file with a .WAV extension didn’t work very well with Sony’s SoundForge because it would down-mix 5.1 to just 2 channels and the clip length seemed to vary slightly. I found this solution while trying to edit movies for language. The nice part about editing only one channel of a 5.1 AC3, is that I can keep the background noise while muting the voice.
Audacity has always been pretty ugly and clunky although it offers amazing capabilities. With their beta version 1.3, it is now possible to open, edit any channel, and save while preserving all the channels. There is a beta version for Windows, Mac, and Linux.
To do this, you’ll need to grab the beta version 1.3 on SourceForge here: http://audacity.sourceforge.net/download/.
Download and Configure FFMPEG
After installing Audacity 1.3, you need to open the “Preferences” from your menu bar and go to “Libraries”. From there you need to click the “Locate” button for FFMPEG. Download and install the operating system appropriate FFMPEG.
Back in Audacity’s Preferences > Library, click the “Locate” button and it will tell you it found FFMPEG automatically.
Change Default Settings
Finally, you need to setup Audacity to save AC3 files while keeping intact all original channels. Go to Preferences > Import/Export and choose “Use custom mix (for example to export a 5.1 mulichannel file)”.
Open AC3/DTS Files
Open your sound file. This will take around 5-6 minutes for a typical 2 hour movie. Make your edits on the channel of your preference.
How to Save/Export
Go to File > Export, then change “Format” to “AC3 Files (FFmpeg)”*. Make sure to click “Options…” and set the bit rate to your desired value. After pressing Save, it will ask you the channel configuration. If you want to keep it like your original, just accept the default. This will take 10-20 minutes for a typical 2 hour movie.
*As of this writing, I have not seen a way to export in DTS format, but if you know a way, leave it in the comments.