It there a PC-based AAC 5.1 channel encoder ?

Or where can I find AAC 5.1 channel sequence ?

PC based 5.1 AAC Encoder's include the Nero codec, and (I think) the Compaact codec.

Nero AAC is included with the Nero 6 software package. Compaact can be found here.

IIRC, channel order is:
1 - Center Front
2 - Left
3 - Right
4 - Left Surround (Rear)
5 - Right Surround (Rear)
6 - LFE

BeSweet (BSN part) help multichannel encoding with nero aac a lot easier.
http://dspguru.doom9.org/

I have done this before, but can remember how. i think it was with nero. however, i do remember that there was not much deference between the file size from ac3 to aac 5.1, unless you choose a really low bitrate

File size is directly related to bitrate, so *of course* you only get smaller files if you use a lower bitrate.

I understand garf. I was just trying to say, you are better off with 5.1 ac3 files. there is not much point transcoding to 5.1 aac/mp4 files at transparent bitrates

FAAC can also encode to 5.1. And Psytel AACenc, althout it reportedly has a bug on multichannel encoding.

Those can't do HE-AAC though, which you probably want for 5.1.

You can get the filesize in half, but indeed no spectacular savings should be expected for lossy to lossy transcoding.

if you are aiming at buying one of the upcoming standalone dvd/mp4 players, able to handle multichannel aac (not explicitely he-aac) you might want to NOT use he-aac for multichannel, as the player will only play it with "low" quality

If your player can't do HE-AAC I wouldn't bother transcoding at all.

so you would waste 448kbps for keeping .ac3? i would prefer lc-aac at the half bitrate