mkv with 5.1 aac won't convert

[BeardFan]

I have this mkv file that contains 5.1 aac audio. VLC plays it fine but it seems impossible to convert it. The video track converts fine, but the audio fails. ffmpeg says it can't resample anything with more than 2 tracks. mencoder does something, but then produces an error and the resulting (unfinished) new audio is unusable, kind of strange slo-mo ghostly sounding.

If I extract the audio with mkvextract, it says 'A_AAC/MPEG4/LC/SBR' as codecID. The resulting "raw" .aac file plays fine in VLC and RealPlayer 10, but ffmpegX won't recognize it.

So is there any way to convert the 5.1 aac sound to AC3 with ffmpegX (or any other share- or freeware tool)?

[major]

You may try to send me a link to download your clip and I will test.

[BeardFan]

I've sent you the link. Hope, you can figure out what the problem is.

[BeardFan]

OK, here's a workaround for this problem:

You need mkvextract to demux the mkv. Also you need FAAD 2 for Mac. In the terminal demux the movie like this:

mkvextract tracks movie.mkv 1:movie.divx 2:audio1.aac 3:audio2.aac 4ubs.srt

Than convert the raw aac files in the terminal with FAAD with the -d option to convert 5.1 to 2 channel:

FAAD_OSX -d audio1.aac

resulting in a audio1.wav file that can be converted easyly to mp3 with ffmpegx, Audacity or iTunes.

Then mux the movie.divx and the audio.mp3 to an avi in ffmpegx and the resulting avi can be converted to DVD (or any other format) also using the extracted subtitle file.

[thoughton]

OK, here's a workaround for this problem:

You need mkvextract to demux the mkv. Also you need FAAD 2 for Mac. In the terminal demux the movie like this:

mkvextract tracks movie.mkv 1:movie.divx 2:audio1.aac 3:audio2.aac 4ubs.srt

Than convert the raw aac files in the terminal with FAAD with the -d option to convert 5.1 to 2 channel:

FAAD_OSX -d audio1.aac

resulting in a audio1.wav file that can be converted easyly to mp3 with ffmpegx, Audacity or iTunes.

Then mux the movie.divx and the audio.mp3 to an avi in ffmpegx and the resulting avi can be converted to DVD (or any other format) also using the extracted subtitle file.

Nicely done I'll be using this fairly often. Thanks.

[BeardFan]

But now I've encountered a new problem. The divx inside the mkv is slightly messed up with the framerates. ffmepgx says it's 25 fps inside the mkv, but the extracted movie wrongly says NTSC framerate (thus being much shorter). And when you calculate the framerates by dividing the actual frames by the supposed running time you get something weird like 24,1005 (no! it's not NTSC film, then the movie would be too long). So I forced the calculated framerate into the avi header, resulting in the same duration as the audio, but still the muxed avi has a slight desynch.

Which leaves the conclusion that mkv might be a nice container in theory, but in the real life, where I want to play the movies on my divx capable standalone, mkv is utter crap!

So is there a tool to force-synch the video and audio to exactly the same duration?

[thoughton]

Quicktime Pro with its "add scaled" command might work. Don't forget to add the video to the audio and not the other way around.