[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

This appears to be missing a semicolon, on line 4.

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

I'm going to explain how this work:

1. It changes the current working directory (folder) to where your m4a are located.
2. It creates a directory named "out" in the current directory
3. It iterates for every m4a file in the folder and it will a) check for the original bitrate, b) copies the id3 tags.
4. After getting the data of one file, it starts to encode the audio to mp3

Can this be done on a mac?

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"