I have hundreds of sound effects - clips just a few seconds long each - that are all m4a files.

I need to convert them to mp3 files. What's the best way of doing this? I see Automator can automate some conversions, but m4a to mp3 isn't one of them.

Is there a good free program or command line utility or something I can use or this? Is there maybe some way I can get QuickTime or iTunes to quickly do this conversion for me?

I can load an NSSound using an m4a... I don't see any way to get NSSound to spit out a file, though...

2 Answers 2


You could install ffmpeg, a command line tool for audio/video conversion, and then create an Automator service invoking a shell command.

For installation of ffmpeg please refer to their website. Once you have installed it, find out the location of it with this command:

$ which ffmpeg

Then, open Automator, create a new Service, change the dropdown menu "Service receives selected" to "files or folders" in "Finder", then add the action "Run Shell Script". Select Pass input "as arguments" and in the textbox, write

for f in "$@"
    /usr/local/bin/ffmpeg -i "$f" -acodec libmp3lame -ab 128k    "${f%.m4a}.mp3"

where you replace /usr/local/bin/ffmpeg with the path to ffmpeg on your computer. That's it!

Now, you can open the Finder, go to a directory containing *.m4a files, select files you want to convert, right-click, go to Services and select your newly created service. There will be no progress bar shown, but ffmpeg will convert your files one after another.

Automator Service screenshot


I'd go with either Max [my personal favourite] or XLD.
Both are freeware.

Both can handle many to many formats, including all the usual suspects, WAV, AIF, MP3, AAC, OGG & many other more esoteric ones.

My preference for Max is 1) I've used it a lot longer which gives it familiarity, but 2) because I can drop a selection of files to it & then decide what to do with them, including whether I need to tweak the ID Tagging.
XLD you have to make your mind up first, then just drop files to its icon in the dock.

  • I think I'm going to go with XLD since it appears you can use it from the command line... although it seems a bit weird since in the options section it says it only supports wav, aif, and two other formats I've never heard of... but then way down in the patch notes it says they added support for mp3. Oh well, I'll give it a try later today and see what happens. Mar 1, 2016 at 13:31
  • XLD doesn't seem to recognize .mp4 files as being audio files... from the command line, I get the message error: cannot handle file. If I use the GUI for the app and do File > Open..., it tells me Error Cannot open the input file. Too bad - that had so much promise with its command line interface. Mar 28, 2016 at 2:01
  • mp4 is a video format, though. You'd need something to extract the audio from it first. I've used mediahuman.com/audio-converter previously for that task, but not in a long time
    – Tetsujin
    Mar 29, 2016 at 8:07
  • You're right - that was a typo when I said .mp4 in the comment. I meant .m4a, as I said in my original post. Mar 29, 2016 at 13:34
  • Yes, can confirm... back to Max then - I've always preferred it anyway ;)
    – Tetsujin
    Mar 29, 2016 at 13:38

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