[How to Convert m4a Files to mp3, Preserving Bitrate and ID3 Tags Using ffmpeg] #ffmpeg #bash

batch-m4a-to-mp3.md

How to convert m4a files to mp3, preserving bitrate and id3 tags using ffmpeg

Prerequisites

1. ffmpeg
2. cygwin (on windows)

Commands

cd /path/to/m4a/files
mkdir out
for f in *.m4a; do 
    ffmpeg -i "$f" -ab `ffmpeg -i "$f" 2>&1 | grep Audio | awk -F', ' '{print $5}' | cut -d' ' -f1`k -map_metadata 0 -id3v2_version 3 -write_id3v1 1 "out/${f%%.*}.mp3"
done

References

http://blog.kdecherf.com/2012/01/14/ffmpeg-converting-m4a-files-to-mp3-with-the-same-bitrate http://jonhall.info/tips_and_tricks/id3_tags_on_windows_using_ffmpeg

I'm not sure if the commands used in Mac is 100% the same in linux, but perhaps with correct dependencies it is possible on Mac, and also possible in windows with some command changes.

This command assumes there are no periods (.) in the filenames other than for the extension. Bad assumpition!
Replace:
"out/${f%%.*}.mp3"
with
"out/${f%.*m4a}.mp3"