I have asked this question before on various forums but never got a suitable answer. I understand that Apple's .m4a files are basically .aac files but with some subtle (or not) differences. I am looking fora way to convert from .aac to .m4a without decoding and re-encoding. Surely this must be possible? Anyone here know how?
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I might be wrong but I had the impression that m4a files are containers. They are similar to mp4 files but only contain audio, whereas mp4 can also contain video. I have also read that an mp4 file which contains only aac audio is identical to the m4a file containing the same aac audio.
Anyway, I use the command line utility "Mp4Box" which can convert to and from aac, mp4, m4a, wave, etc. As far as I know it doesn't decode/re-encode when converting aac to either mp4 or m4a.
I have set up a "drag and drop" batch file in the folder which I use for the editing of aac files and then created a shortcut to that batch file and, finally, copied that shortcut onto my Desktop.
To use it I have Windows Explorer only occupying part of the screen and merely drag and drop the aac file onto the icon (on my Desktop) for the batch file. The mp4 or m4a file is created in the same folder as the aac file, with the same name as the aac file (apart from the filetype, of course).
That batch file creates mp4 files but changing the "mp4" to "m4a" in the above batch file should result in m4a instead of mp4 files.REM Batch file to convert aac to mp4
set FILE=%~n1
F:\Music_Misc\aac_tools\MP4Box-0.4.6\MP4Box -add "%FILE%.AAC" "%FILE%.mp4"
PAUSE
Notes:
set FILE=%~n1 - sets FILE to the name of the file that is dropped onto the batch file shortcut icon
F:\Music_Misc\aac_tools\MP4Box-0.4.6\MP4Box - is the path to the location of Mp4Box.exe
PAUSE - gives the chance to see any error messages before closing the window.
The double quotes enable the batch file to cope with filenames that include spaces.
PS There are graphical user interfaces for Mp4Box but I've never used them so can't comment.
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