How to merge multiple MP3 files

You’d think it would be very easy to combine multiple MP3 files into one, while preserving all the ID3 tag metadata and without re-encoding the audio (which is lossy). Well, it actually isn’t that hard at all.

There is a handy command-line utility for combining MP3 files, mp3wrap. Unfortunately, it doesn’t correct the audio duration tags/headers (so iTunes/iPod will only see the first part of the file), and it clobbers your ID3 tags with its own (so that the file can later be unmerged with mp3split — this is a “feature”).

There’s also the easy cat solution:

cat 1.mp3 2.mp3 > all.mp3

But it doesn’t correct the duration, either. Maybe you don’t care about ID3 tags, and your playback software doesn’t care about a wrong duration header (some ignore it)? But if you want to get your MP3 files right or you’re using something like iTunes, here is how it is done.

Install mp3wrap, ffmpeg and libid3 if you don’t have them already.

The following combines 1.mp3, 2.mp3 and 3.mp3 into all.mp3, and copies ID3 tags from 1.mp3:

mp3wrap tmp.mp3 1.mp3 2.mp3 3.mp3
ffmpeg -i tmp_MP3WRAP.mp3 -acodec copy all.mp3 && rm tmp_MP3WRAP.mp3
id3cp 1.mp3 all.mp3

Here’s what’s happening:

  1. mp3wrap merges the files. Unfortunately, it also leaves wrong file duration headers and clobbers any original ID3 tags.
  2. ffmpeg fixes the file duration. You could also use something else, like mplayer/mencoder (-oac copy option) here.
  3. id3cp copies the ID3 tags from 1.mp3 to all.mp3

If you have problems with ffmpeg, a little program called vbrfix can be used instead:

mp3wrap tmp.mp3 1.mp3 2.mp3 3.mp3
vbrfix -ri1 -ri2 -lameinfo tmp_MP3WRAP.mp3 all.mp3 && rm tmp_MP3WRAP.mp3
id3cp 1.mp3 all.mp3

lameinfo is specified in the command because Lame had been used for the encoding of the original files, before using mp3wrap to combine them.

You can also substitute the first line of code for this, in order to wrap all files in the folder together:

mp3wrap tmp.mp3 *.mp3

If you have a lot of files to merge, you might run into the shell expansion limit by using a wildcard. If so, us the xargs trick:

$ find -name \*mp3|xargs mp3wrap all.mp3

There is yet another way, without going through mp3wrap:

cat file list... | ffmpeg -f mp3 -i -acodec copy outfile.mp3

And then the id3 copy command.

4 responses to “How to merge multiple MP3 files”
  1. bread says:

    I am sorry if this is a lame question, and forgive my lack of knowledge, but is it at all possible to keep all the ID3 tags for all the .mp3 files?

    • practic says:

      The tags of the Mp3 apply to the file. So if you only have one Mp3 file, that’s only one set of tags. I suppose you could try to concatenate the tags, but I’m not sure how you would make it meaningful. Perhaps one thing that might help is to use a GUI program like Kid3, which allows you to export the tags to different file formats. If you did that before you join the Mp3’s into one file, you’d at least have a way of saving them.

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