How to extract an ac3 audio track out of an Xvid avi file?

[Falcon500]

How do I extract (demux I guess you would call it) an ac3 audio track out of an Xvid avi file? Is there some program that would allow me to do this?

[terryj]

I wouldn't demux, I would just re-record the audio
to AIFF, 48khz, 16bit with either Wiretap, Audio Hijack
or Audio HiJack Pro. Since most AC3 files you get
from the internet are suspect, and can cause headaches
down the line, you'd be better off just re-recording the
file.

[TugBoat]

You could use ffmpegX to extract it. Open the movie, select the 'movie audio to AC3' preset, then choose 'passthrough' in the audio tab. Seems to work and A.Pack opens the AC3 normally. Like Terry said though, it could be corrupt. I guess if it plays fine on your target device it doesn't matter. Unless you then try to Downmix it with A.Pack, and get one of those errors like 'missing word(s)' like I've gotten from outside sourced AC3s....
8)

[terryj]

Tug, that's EXACTLY what got me on the track of
"just re-record it."
Ya know bit torrent and p2p , and usenet are great tools,
and i'm all for people using their computers and learning
as much as they can, but when they start sharing
items that aren't "up to snuff"...it almost makes me wish
for some kind of regulation...

[thoughton]

Some avis have 5.1 ac3 sound though. Personally I like to keep those rather than downmix to stereo ffmpegX is your friend. For me DVDs are mostly about 5.1 sound, and less about the picture quality (which to my aging eyes seems no better than laserdisc). I would never ever downmix 5.1 to stereo unless I had absolutely no other choice (and I can't really believe you are really suggesting people do that without trying anything else first).

I also don't agree that "most" ac3s off the net are suspect. In my experience a small minority of them have problems.

[terryj]

I also don't agree that "most" ac3s off the net are suspect. In my experience a small minority of them have problems.

How about I re-prhase this to:
"Most AVI's on the net are suspect."
Surely you would agree with that....
8)

guess we must just be looking in diffrent places across the
wide, wide internet my friend....

[JoeRodr]

why not just use quicktime and extract the audio track.. that usually works best for me w/ avi's

[Falcon500]

Quicktime doesn't recognise AC3 audio files so you have to save the audio in a .mov container making it incompatible with most DVD authoring software...

[chesneychrist]

Hi,

I'm attempting to do what Falcon500 asked in the first post. As suggested, I used the "Movie audio to ac3" option, and set the codec to "Passthrough".

The result is a file with the same name as the avi file with an added "ff" suffix. The file plays in VLC, but is this a useable ac3 file?

Also, have several files to convert, and was planning on using sizzle to author a DVD once I have the audio extracted and video encoded. As far as I can see though, sizzle won't accept ac3 files. So am I on the right track, is it possible for sizzle to use the extracted ac3 audio?

Thanks.

[rumplestiltskin]

There is a later QT AC3 codec that does work.

[chesneychrist]

Thanks. I've just grabbed the new codec, I'll give that a try.

I might not need it though. I've found if I encode to DVD using mpeg2enc, set the audio to passthrough, and use decode with mplayer, I end up with mpv and mpa files.

Sizzle seems to recognise both these files, I'll see how it goes.

Cheers.