how do I demux an MP4?

[exekutive]

I just need the aac audio stream from it.

[emmgunn]

MKVtools will extract tracks from mp4's as well as mkv's. It's trialware, but you don't need to register it to do what you want. I wouldn't be surprised if AVIdemux also lets you extract tracks from an mp4.

[exekutive]

Thanks, I'll give MKVtools a try. I've already tried AVIdemux and it produced an unusable file.

By the way, the download link (http://www.emmgunn.com./downloads/mkvtools2.4.4.zip) is just taking me back to the homepage.

[exekutive]

Solved!

OK so I downloaded it with the hotfile link instead, and it worked. Extracted my audio stream in seconds. Thanks emmgunn. I think this is currently the only app for mac that does this reliably.

[Case]

By the way, the download link (http://www.emmgunn.com/downloads/mkvtools2.4.4.zip) is just taking me back to the homepage.

That happened to me too with the link in your post. But by going to the download page first, the link MKVtools 2.4.4 did start a download for me.

[exekutive]

I was using the download page as well. (Google Chrome) But I just tried it again and now it works. Strange.

edit: aha, the extra "." in the URL has been taken out. Someone must be listening

[rumplestiltskin]

QT Player Pro will extract the audio without a problem as will MPEG Streamclip (and a few dozen other apps).

[exekutive]

Those are the first two apps I tried, in that order, to no avail. I can provide the source file to you if you want to try.

Also, several apps have an option to convert the audio, but not to demux it as is.

[Case]

for AAC audio in the source file:

ffmpeg -i sample.mp4 -vn -acodec copy sample.m4a

for AC3 audio in the source file:

ffmpeg -i sample.mp4 -vn -acodec copy sample.ac3

[exekutive]

for AAC audio in the source file:

ffmpeg -i sample.mp4 -vn -acodec copy sample.m4a

for AC3 audio in the source file:

ffmpeg -i sample.mp4 -vn -acodec copy sample.ac3

Interesting, Case. Can that also be done with the ffmpegx front end?

[Case]

Can that also be done with the ffmpegx front end?

Sort of. Not in the GUI, but you could use the ffmpeg binary inside the application package.

Use the command line, but instead of "ffmpeg", "sample.mp4", "sample.m4a", write the full path. Or use drag-and-drop, like this:

In the Finder, navigate to ffmpegX. Control-click the application, hold down the mouse until you get the contextual menu. Select Show Package Contents. Open the Contents folder. Open the Resources folder. Find the ffmpeg binary there. Keep this last window open.
Open Terminal. Drag the ffmpeg binary to the Terminal shell window. Terminal will translate this action to the full path to ffmpeg. Type "-i " (with a space at the end). Drag-and-drop your source file. Type "-vn -acodec copy " (with a space at the end). Drag-and-drop your source file again. Backspace a few times to delete the last "mp4", then replace it with the wanted suffix. Hit <enter>. Done.

[exekutive]

Hi Case. I tried it your way, just for shites and giggles.

Joes-MacBook:~ joe$ /ffmpegX/ffmpegX.app/Contents/Resources/ffmpeg -i /Users/joe/Desktop/Jaia.mp4 -vn -acodec copy /Users/joe/Desktop/Jaia.m4a
FFmpeg version CVS, Copyright (c) 2000-2004 Fabrice Bellard
Mac OSX universal build for ffmpegX
  configuration:  --enable-memalign-hack --enable-mp3lame --enable-gpl --disable-vhook --disable-ffplay --disable-ffserver --enable-a52 --enable-xvid --enable-faac --enable-faad --enable-amr_nb --enable-amr_wb --enable-pthreads --enable-x264 
  libavutil version: 49.0.0
  libavcodec version: 51.9.0
  libavformat version: 50.4.0
  built on Apr 15 2006 04:58:19, gcc: 4.0.1 (Apple Computer, Inc. build 5250)
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/Users/joe/Desktop/Jaia.mp4':
  Duration: 00:09:51.8, start: 0.000000, bitrate: 479 kb/s
  Stream #0.0(und): Audio: aac, 44100 Hz, stereo
  Stream #0.1(und), 25.00 fps(r): Video: h264, yuv420p, 480x360
Output #0, mp4, to '/Users/joe/Desktop/Jaia.m4a':
  Stream #0.0: Audio: aac, 44100 Hz, stereo
Stream mapping:
  Stream #0.0 -> #0.0
Press [q] to stop encoding
size=    9274kB time=591.9 bitrate= 128.4kbits/s    
video:0kB audio:9074kB global headers:0kB muxing overhead 2.201532%

It produced a 9.5MB file, but I'm unable to play it.

[emmgunn]

If you're looking for more giggles, and you're OK with the command line you could try using mp4box. You can find it inside of ffmpegx using Case's instructions. You'll find good instructions for it's use here.

[exekutive]

you could try using mp4box

It worked! Like this...

mp4box -raw 1 inputfile.mp4
Extracting MPEG-4 AAC

... and it was the quickest way so far. It's really a shame that you can't do more things like this with the GUI.

[exekutive]

This is going a bit off-topic, but since we're on a roll...

How can I do the same thing with an FLV?

[exekutive]

One way is to first convert it to MP4 using MPEG Streamclip. (I'm pretty sure this doesn't touch the streams and just re-wraps them in a different container.)
Then, use either of the two methods above (MKVtools or MP4box).

Maybe there's a one-step way to do it?

[emmgunn]

Going command line again, I haven't used ffmpeg much, but it should be able to do it. I have had success using mplayer, so you can try that too. Just google mplayer and dumpaudio and you should find plenty of help. You can find mplayer inside a number of of apps, just like you found mp4box. MKVtools has a fairly recent version, but probably the best would be to find the most recent copy of one of the versions of the mplayer gui.