AC3 Encoding with Compressor 2

Hi all --
Anyone know why Compressor 2 won't convert my MPG audio streams to AC3?
I demuxed an MPG-2 program stream to .m2v and .mpa elementary streams.
The .m2v plays fine -- the .mpa must first be converted to 48kHz AIFF before Compressor will convert it to AC3.
Wish I could skip that intermediate step -- anyone know how?
Thanks -- Jerry
Dual 1.25GHz G4   Mac OS X (10.3.9)  

Thanks everyone.
So here's a related question:
I've used MPEG Streamclip in the past --
When I do "Demux to M2V and AIFF" on a clip,
the AIFF comes out fine... but the M2V is a program stream, not elementary!
In other words, it's not a true demux, because the M2V still has an embedded audio stream!
Anyone know a fix for this, or can explain why this happens?
Thanks again for your support!
-- Jerry

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    Test with Encore:
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    If you don't know what that is, or how to do it, it is very simple.  Go to: http://www.slysoft.com/en/ and download "Virtual Clonedrive."  It is free.  It tricks your operating system into thinking you have another physical DVD drive.  In fact, it can create up to 8 virtual drives.  Now you don't have to waste time burning, and erasing DVD's every time you make a change to a project.  You can build your project as a DVD Image from Encore, save the .iso file to your Desktop and "mount" it (load it) in Virtual Clonedrive.  You're computer will now think you loaded a DVD into a physical drive, and launch whatever DVD player you have installed.  Mine launches "Cyberlink PowerDVD" which plays the AC3 audio-only DVD in full surround sound on my computer. 
    Building and testing projects this way will save you endless hours.  If you need to make a quick change, just "Unmount" the .iso in Virtual Clonedrive, rebuild your project to the same filename, and "Mount" it again.  Instant testing!
    Now, as promised, back to that LFE Channel problem with Premiere that I mentioned:
    Audacity will let you modify the individual channels in your interleaved 6-Channel file.  So don't put anything in that channel in your Premiere mixer. Leave the "Bass Clef" knobs at full CCW position ( -00 db ).  The bass from the other channels will go to your subwoofer automatically in your Amplifier.
    Now if you have some low frequency effects files, open them in Audacity.  You can open multiple instances of Audacity at the same time by going to "File > New."  Then, copy and paste them into the LFE Track at the correct point.
    Audacity newbie Hint:  Audacity doesn't yet have a "Mix-Paste" function, so to avoid altering the track length as you paste in your clips, do the following: Select the LFE track by clicking on it's info area.  The info area should say something like "Mono, 48000Hz"  Then press "Delete," That will remove everything from the track.  Now copy and paste your clips into the track by clicking once with the "Selection Tool" where you want the clip to start, and selecting "Edit > Paste."  If you need to fine tune the position of the pasted clip, use the "Time Shift Tool" to move it left or right.  If you work from left to right, then you won't push clips over when you paste new ones in.
    There is another way to do this by opening up new tracks, using the "Mix and Render" function, and re-ordering the tracks to maintain the L,R,C,LFE,LS,RS channel order.  But that's for advanced users.
    Where to get thumpy effects?:
    Remember, Audacity will open DVD ".vob" files.  Just remember to get permission from the copyright owner.  HeHe.
    PS If you can't get your surround sound to work with Premiere on your computer, see my other tutorial.

    After further research, there is a better AC3 encoder out there than the FFMPEG that Audacity uses.  It is a more sophisticated implementation of the format.  Unlike FFMPEG, it uses floating point numbers instead of integers internally, among other things.  It is also updated periodically.  Although the pace is glacial.
    You can read about it here: http://aften.sourceforge.net/
    The easiest way to use it is with a graphical front-end like "wavtoac3encoder" found here: http://code.google.com/p/wavtoac3encoder/
    You don't need to change anything from the default settings.
    Just follow my tutorial above and instead of using Audacity to create the AC3 file after you are done editing, output the multi-track file in .wav format uncompressed from Audacity.  Then drag and drop it into "wavtoac3encoder"and create your file.
    If you don't need to edit the multi-track .wav file from Premiere in Audacity, then just drag and drop that file into "wavtoac3encoder" and encode.
    The quality, although probably not as good as SurCode, sounds good to me.
    Remember, this is strictly for non-commercial use.

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