Convert m4a to mp3 on OS X command line using ffmpeg

gistfile1.txt

brew update
brew link yasm
brew link x264
brew link lame
brew link xvid

brew install ffmpeg

ffmpeg wiki: 
https://trac.ffmpeg.org/wiki/Encode/MP3

lame option 	Average kbit/s 	Bitrate range kbit/s 	ffmpeg option
-b 320 	320 	320 CBR (non VBR) example 	-b:a 320k (NB this is 32KB/s, or its max)
-V 0 	245 	220-260 	-q:a 0 (NB this is VBR from 22 to 26 KB/s)
-V 1 	225 	190-250 	-q:a 1
-V 2 	190 	170-210 	-q:a 2
-V 3 	175 	150-195 	-q:a 3
-V 4 	165 	140-185 	-q:a 4
-V 5 	130 	120-150 	-q:a 5
-V 6 	115 	100-130 	-q:a 6
-V 7 	100 	80-120 	-q:a 7
-V 8 	85 	70-105 	-q:a 8
-V 9 	65 	45-85 	-q:a 9

ffmpeg -i in.m4a -codec:a libmp3lame -qscale:a 1 out.mp3

Thank you for this. I created a macOS "Quick Action" out of this in Applescript/Automator (with "audio file in Finder" as input)

on run {input, parameters}
	tell application "Finder"
		set fileAlias to input as alias
		set fileName to name of fileAlias
		set fileExtension to name extension of fileAlias
		set AppleScript's text item delimiters to "."
		set title to text 1 thru text item -2 of fileName
		set theInputFilePath to POSIX path of fileAlias
		set theOutputFilePath to text item 1 of theInputFilePath
		set convert to do shell script "/usr/local/bin/ffmpeg '" & theOutputFilePath & ".mp3" & "' -i '" & theInputFilePath & "' -codec:a libmp3lame -qscale:a 1"
		set theOutput to theOutputFilePath & ".mp3"
	end tell
        return theOutput
end run

on run {input, parameters}
	tell application "Finder"
		repeat with fileitem in input
			set fileAlias to fileitem as alias
			set fileName to name of fileAlias
			set fileExtension to name extension of fileAlias
			set AppleScript's text item delimiters to "."
			set title to text 1 thru text item -2 of fileName
			set theInputFilePath to POSIX path of fileAlias
			set theOutputFilePath to text item 1 of theInputFilePath
			set convert to do shell script "/usr/local/bin/ffmpeg '" & theOutputFilePath & ".mp3" & "' -i '" & theInputFilePath & "' -codec:a libmp3lame -qscale:a 1"
			set theOutput to theOutputFilePath & ".mp3"
		end repeat
	end tell
	return theOutput
end run

thanks , I change the code with "Get Selected Files in Finder" as input to support multi files (on my laptop , MacOS Monterey version 12.5 )

however, I not know how to work with "audio file in Finder" as input, thanks so much if have your reply @atchoo78

Hi! Thanks for the modified code. Sorry I wasn't clear on this. What I meant by that is this:
I created a new document in Automator, chose the "Quick Action" document type and the "AppleScript" action with the actual script. I configured the "Quick Action" like this in Automator:

That's what I meant by

"...with "audio file in Finder" as input"

Andreas 🙂

I wonder why the size increases so much?

I had an m4a of size: '124943', and the output of the command given above produced an mp3 of size: '518403'
Seems odd.