Direct AAC -> AC3 5.1 conversion?

[cwapface]

I have matroska files that have h264 video, aac 5.1 audio, and subtitle tracks on my linux box. I'd like to use mencoder to convert the audio to 5.1 ac3 for my receiver to decode, but I can't quite figure all this out. If I do a:

mencoder -ovc copy -channels 6 -oac lavc -lavcopts acodec=ac3:abitrate=384 -o out.avi input.mkv

I get an avi that won't play smoothly with ac3 that has the FL and C channels swapped, and no subtitles. I tried using mkvmerge to use the original video and subs streams while muxing in the new ac3 audio:

mkvmerge -o new.mkv -A input.mkv -D -S out.avi

mkvmerge v1.8.0 ('Wise Up') built on Nov 12 2006 20:41:21
'input.mkv': Using the Matroska demultiplexer.
'out.avi': Using the AVI demultiplexer. Opening file. This may take some time depending on the file's size.
'input.mkv' track 1: Using the MPEG-4 part 10 (AVC) video output module.
'input.mkv' track 3: Using the text subtitle output module.
'out.avi' track 1: Using the AC3 output module.
The file 'new4.mkv' has been opened for writing.
progress: 29%

When this gets to 99%, it spits out a few thousand lines of messages:

Packet 72881, timecode 1314114000000, bref 1329342000000, fref -1
Packet 72882, timecode 1314148000000, bref 1329384000000, fref -1
Packet 72883, timecode 1314214000000, bref 1329426000000, fref -1
Packet 72884, timecode 1314248000000, bref 1329510000000, fref -1

and I'm left with an 81kb new.mkv that is good for nothing.

Is there an easier way to do this that works and maps channels correctly, while keeping the subtitle tracks in there? I just want a mkv file with a new audio track.

[shon3i]

Use BeHappy with BassAudio to decode AAC 5.1 and Aften AC3 encoder.

[xaeroak15]

you can use Nero's encode function ,remember packed the maosou's plugin to convert aac-->ac3

[cwapface]

Originally Posted by xaeroak15

you can use Nero's encode function ,remember packed the maosou's plugin to convert aac-->ac3

I don't know what this means????

I've installed nero 8 ultimate, but can't find any info about maosou or what to do with his plugin.