Exporting AAC audio with multiple channels

[Mr Wolf]

Hi all!
I extracted an AAC audio track from a mkv with MKVExtractGUI2. The track is 5.1 channels. What I want to do is to add a bit of silence at the beginning to syncronize it and merge it in another mkv, but when I export it with Audacity (Audacity 2.0.6, Windows 7 64 bit) the channels are mixed in a mono track; otherwise, I can export multiple tracks individually.
I searched a bit, but I couldn't find a way to make the modification I need and export it has a 5.1 track.

Thanks in advance.

[Gale Andrews]

Change to "Use custom mix" in the Import / Export Preferences.

Gale

[Mr Wolf]

Thanks!
Perhaps, I'm doing something wrong, but I get a 0 KB file. (I've not selected the silence I added at the beginning)
I tried to convert to mp3 (stereo) and it worked.

[Gale Andrews]

Thanks!
Perhaps, I'm doing something wrong, but I get a 0 KB file. (I've not selected the silence I added at the beginning)
I tried to convert to mp3 (stereo) and it worked.

Yes I should have mentioned this - if you tried AAC multi-channel export using "M4A (AAC) Files (FFmpeg)" or "Custom FFmpeg Export", it will fail because the default libvo-aacenc AAC encoder which the "recommended" FFmpeg uses only supports stereo.

And the standard MP3 specification only supports stereo.

WAV (very large) or AC3 export will give you a multi-channel file.

Alternatively, you can use the FFmpeg native AAC encoder instead which supports multi-channel export if you don't mind exporting using "(external program)" and typing out a command: http://forum.audacityteam.org/viewtopic ... 56#p272756.


Gale

[Mr Wolf]

Ok, to be clear, you're not talking about this:
http://lame.buanzo.org/
?

I've this installed.

[Gale Andrews]

Ok, to be clear, you're not talking about this:
http://lame.buanzo.org/
?

I've this installed.

I know you have LAME installed or you could not have exported MP3. But as I said, the standard MP3 format does not support more than stereo.

As I said, to export as multi-channel you can export as WAV or AC3. If you prefer to export as multi-channel AAC, then you must choose "(external program)" and type out the command that tells Audacity to use the native FFmpeg encoder. As it says in the link I gave , you can use a command like either of these two:

Code: Select all

ffmpeg -i - -strict experimental -c:a aac -b:a 240k "%f"

Code: Select all

ffmpeg -i -  -strict experimental -c:a aac -q:a 10 "%f"

Change the "240" in the first command if you want a different bit rate, or if you use the second command, change the "10" if you want a lower quality (10 is the maximum quality).

If you export as WAV or AC3, you will need to check the exported file to be sure you have the channels in the correct order when you play the file in your surround system. If not, you can drag the tracks in Audacity up or down to the correct position then export again. Drag in the panel to left of the blue waves.


Gale

[Mr Wolf]

Ok! Many thanks!