Correcting badly encoded 5.1 top proper channels... easily?

[cinesimon]

Hi all - I have a couple commercial DVDs and a 720p avi with AC3 audio which seem to have the same issue - they appear to have been badly encoded: the center channel is coming from the right front channel, and vice-versa. The other channels all seem to be fine. It's the same with all three films.

I'm looking for an application where I can load an AC3 file(or mka after I've removed video using mkvmerge) - firstly extracting the DVD .iso files to vts, then putting them through mkvmerge so they're a whole mpeg and an AC3 within an mkv(instead of 1gb chunks as vts files are) - then remove the video again with mkvmerge, so there's only an mka (AC3) left... hope that makes sense!

So anyway - is there a simple app, or pair of apps, which I can load an mka with AC3, and simply tell it what each channel will become on output? Like a 'drop-down menu' channel selector - for each audio channel? That kind of idea, anyway.

Thanks in advance for your help - I'm not hugely knowledgeable, but in some areas, I have pretty good knowledge of some simple programs such as mkvmerge and (with some functions) Popcorn Audio Converter - so talk to me like an semi-idiot who knows some but not all. If you get my drift.

Thank you in advance for any help!

[themediaman]

Have you came to this conclusion just from listening to the track?


I cant think of anything that could do what you are looking for................

Make sure your wiring to the reciever is correct and that its up to date firmware wise..........

Then you could try obtaining another 5.1 track to compare with your faulty one.........

I usually demux files with tsmuxer, then remux with mkvmerge........

[jagabo]

Audacity with the ffmpeg source filter can import audio from a video file. You can then reassign the tracks and export as AC3. Remux the new audio with the original video.

<edit>
Looks like I was wrong. Audacity muxes the audio down to stereo when exporting AC3.
</edit>

[intracube]

Looks like I was wrong. Audacity muxes the audio down to stereo when exporting AC3.

Under Preferences->Import/Export there's a "Use custom mix" option to export a 5.1 multichannel file.

But I haven't ever done 5.1 sound mixing.

[cinesimon]

Thanks guys.
Mediaman - I have around 4000 films - only three are wrong. Yes, through listening, on my 3 different surround systems, the center channel is coming out of the right speaker, and the right channel is coming out of the center speaker. It is something that happens occasionally - a 'bug' if you like, that is known to happen, very rarely. I have in the past just returned the film for refund(no point in getting a replacement, as they're not a 'bad disc' thing, but a mastering issue - as all discs from the distributor have the same issue). But the two DVDs I have are rare and I cannot get them from another distributor so thought I'd give re-configuring the 5.1 a go, so I don't have to watch them in mono. And rather than rewiring my system to watch the films, I'd rather just have mkv copies of them with the correct audio.

I managed to import the audio using Audacity's 'use custom mix' option - they're now presented, unlabeled, as 6 mono tracks. So I have to figure out which is which somehow(!) and reassign them. Somehow.
Looks a little hit and miss, though I may be able to figure it out.

If anyone has any other suggestions, I'm all grateful ears.

Thanks so much, guys, for responding - much appreciated.

[jagabo]

Aften gets mentioned a lot for AC3 encoding. I believe you can save from Audacity as 6 channel WAV, then use Aften to encode as 5.1 AC3.

[intracube]

I managed to import the audio using Audacity's 'use custom mix' option - they're now presented, unlabeled, as 6 mono tracks. So I have to figure out which is which somehow(!) and reassign them. Somehow.

When you export as a wav, you should get a window where you can remap the audio tracks if necessary:
http://www.hydrogenaudio.org/forums/index.php?showtopic=73497
The GUI is a bit crude, but you select pairs of boxes to link/unlink them.

I couldn't find a definitive answer to what the channel order should be, and it seems to be different between multichannel wav and ac3 files:
http://forum.audacityteam.org/viewtopic.php?f=15&t=11180

Someone also suggested that there's a bug/inconsistency between different versions of Audacity that cause the channels to be mapped differently for ac3.

You'll have to do a bit of trial and error.

[cinesimon]

Wow thanks so much for that - great stuff. Will post later on in my day after I've had a go, to let you know how I get on.

[jagabo]

I enabled "Use custom mix" in the preferences of Audacity so that I could export as a multichannel WAV file.

Ah! That's why audacity was always downmixing on me. After enabling "Use custom mix" I can save six channel audio.
Edit -> Preferences -> Import/Export -> Enable Custom Mix.