m4a2mp3

Shell script to bulk transcode .m4a audio files (e.g. Apple iTunes downloads) to .mp3 files via VLC. Ideal for parents who want to load purchased iTunes music on kids' music players.

Usage

Pass in one or more paths to either .mp4a files or to directories containing them. When directories are provided, the script will search all sub-directories for .m4a files.

Some simple MP3 players don't support special characters like ! in file names, and those without graphical displays use numeric prefixes on filenames to provide a consistent play order. The script thus outputs a sanitized, and numbered, file name in the destination directory. Output directory defaults to $PWD/MP3 but can be set by setting the dst environment variable, e.g.:

dst=$HOME/Music/mp3 -n 10 m4a2mp3 /Path/To/Music/Collection/Albums/Kids\'s\ Greatest\,\ Vol.\ 1/

results in:

/Users/foo/Music/mp3/10_Kids_Greatest__Vol._12_Unicorns__And__Trains_Song__.mp3
/Users/foo/Music/mp3/10_Kids_Greatest__Vol._12_We__Love__Fun.mp3

For reasons I don't really understand, or could find much information on, vlc on macOS will randomly fail when converting a file via a command line. However, retrying the command will eventally work, though it may take more than one retry.

To make life easier, this script does two things. The first: it generates a new script called commands.sh and writes the exact VLC command there. Passing -x will automatically execute the script once generated. And two: because it builds a command that prevents VLC from overwriting an existing file, you can simply re-run commands.sh until all files have been processed. At that point, delete commands.sh otherwise the next time you run m4a2mp3 the new commands will be appended to the end (and you'll probably see a bunch of pointless error messages).