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way to convert .mp4 to .mp3 (or, strip audio from .mp4)?


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way to convert .mp4 to .mp3 (or, strip audio from .mp4)?
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apple007
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Join Date: May 2006
 
2008-09-23, 18:45

I have an .mp4 file that has no video whatsoever but has an audio track I'd like to keep. Does anyone know a good way to either convert an .mp4 to .mp3 format, *or* strip the audio track from the .mp4?

This isn't a big deal, but I'd prefer this "blank" video not reside in my Movies or Music Videos section of iTunes, so I'd like to get it into a true audio format. Thanks very much.
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Dorian Gray
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Join Date: May 2005
Location: Paris, France
 
2008-09-23, 19:18

In QuickTime Pro you could extract the audio (Command-J, select sound track, click "Extract") export as an AIFF (lossless), then drag and drop the AIFF into iTunes. Then convert the file to your standard iTunes import format (Control-click the track, select "Convert Selection to..." from the menu). Then delete the AIFF from your iTunes library.

That would of course involve re-encoding, which is lossy unless you use a lossless encoder in iTunes (in which case the file size would grow about 4x). Extracting is more difficult but can be done with other software. The details would depend on precisely what audio codec is used in the MP4 container and whether it's standards-compliant.

If you're stuck and the file is nothing personal, put it up on savefile.com (free, no registration) and I'll probably figure out a way to extract the audio without re-encoding (tomorrow; it's bedtime on this side of the pond).

… engrossed in such factional acts as dreaming different dreams.
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screensaver400
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Join Date: Jan 2005
 
2008-09-25, 16:21

Quote:
Originally Posted by apple007 View Post
convert an .mp4 to .mp3 format, *or* strip the audio track from the .mp4?
Is it really an MP3 audio track in an MP4 file? I find that most MP4 video files use AAC audio (since AAC is part of the MPEG-4 specification, after all).

I just took an MP4 file I had (H.264 video with AAC audio) and extracted the audio using Dorian Gray's Command-J method above. However, instead of selecting AIFF and converting in iTunes, I selected "Movie to MPEG-4." Under Options, I selected "Pass through" as the Audio Format in the Audio tab.

I then dragged the resulting file into iTunes, and it seems to recognize it as an audio file. I added the title, artist, and the like, and then synced it to my iPhone. It appears in the Music sections, but not in the Video sections.

Assuming that your audio is AAC to begin with, and that you have no particular need to have the track converted to MP3, I think this solution should suit your needs.
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apple007
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Join Date: May 2006
 
2008-09-25, 19:41

Thanks for the tips. I didn't even think that the .mp4 might already have an AAC audio track. The problem is, I don't have QuickTime Pro. Does anyone know of a free app that might accomplish the above? Thanks.
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screensaver400
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Join Date: Jan 2005
 
2008-09-25, 22:56

Quote:
Originally Posted by apple007 View Post
Thanks for the tips. I didn't even think that the .mp4 might already have an AAC audio track. The problem is, I don't have QuickTime Pro. Does anyone know of a free app that might accomplish the above? Thanks.
FFmpeg should be able to do it (the command line version, not ffmpegX). I think I installed it with Darwinports.

You'll need a command like this. It will vary depending on your specific MP4 file, though:

ffmpeg -i "file.mp4" -map 2 -f libfaac -acodec copy audio.aac

(I've actually never used ffmpeg in this way. Someone correct me if I'm wrong.)
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