Noob needs some help

[Flak]

Can someone help me/write me a batch file that will remux/convert an entire folder doing just a copy of the video (h.264 codec) and converting the audio from 6 channel AAC to 6 channel AC3?  And also is possible keeping it in the mp4 container?

My reasoning for this... 
I've been ripping my entire movie collection to my media server.  And have been ripping them to the mp4 container using h.264 and multi channel aac as the codecs.  As I was streaming them to my PS3 and it plays these natively.  However, I've been recently running into some dvds and blu-ray in my collection that are protected by Cinavia and the PS3 of course notices these streams and gives me the error code 3.

So I bought a WDTV Live to play with, which doesn't notice Cinavia.  But it also doesn't stream AAC as LPCM to my receiver, so all AAC is downmixed to stereo.  I was going to get a different media streamer that does output all audio as LPCM like my PS3 does, however in the meantime my wife has fallen in love with the WDTV.  So rather then spend more money on another device I was hoping to just do a mass convert of all my current movies and then new movies going forward I'll just rip with ac3 audio.

Thanks

[Agent_007]

IIRC AVIdemux didn't cooperate with AC3+MP4 combo. (I might be wrong...)

Easiest way is to do that is to create JS script from GUI version and run it for all files.
http://www.avidemux.org/admWiki/doku.php?id=tutorial:batch_processing#combination_of_command-line_and_js_scripting