Splitting Mp3's

caseydk writes: "I'm working on a project that needs to take a single mp3 (a live recording) and play individual sections of it. Preferably, so that the user must only download a portion of the mp3, instead of the whole thing. Unfortunately, most (or all) mp3 splitters that I have found have a gui. I'm looking for something command-line, so that I can just have the server do it during low usage times or (worst case) on the fly. Any suggestions?"

Comments

Re:headerless format

[Anonymous Coward]

A quick google search on "mp3 header" found this document on the mp3 header format. Where I learnt that the beginning of each frame starts with the first 11 bits set to 1, so you can use this to write a quick script to split a mp3 up into pieces.

mpg toolbox

[LinuxGeek8]

You should check out mpgtx, the mpg toolbox.
It's heading for a stable 1.0 release.
You can find it on http://mpgtx.sourceforge.net

By the way, splitters with a gui?
I find it hard to find a mpg splitter with a gui.
I do know mpgcut (or mpcut?) and bc2000.
Which ones are you referring to?

headerless format

[Rebar]

Since MP3 is headerless, you should be able to just calculate where in the file you want to be based on the bitrate, and use 'dd' to cut out a snippet.

I've tried this and it sometimes works and sometimes doesn't depending on the player, since the start of your file snippet will have junk in it, but it seems to me that it would be an easy programming exercise to create a program that would lop off the leading junk until it finds the next valid MP3 frame.

I don't claim to know much about MP3 format, but it appears from a quick session with a hex editor that frames start with 0xfffb9200 - can anyone verify this? If so, you could hack out something in an hour that would be fast, scriptable and do exactly what you want.

For extra credit points, you could then use mp3info to add id3 tags so your file will look cool when playing in xmms or whatever.

I've done this...

[Brazilian Geek]

... using dd.

I know about the MP3 file header but before I knew about it I was chopping MP3s just for kicks. It works, it's easy and knowing the kbps of the file you can calculate the exact point to start and end. Example:

dd if=biggie_file.mp3 of=shortie_file.mp3 bs=1c seek=200k count=150k

It REALLY does work and it's command line - not to mention all the piping possibilites.

Re:Sorry, dd chopped mp3 files do not always work.

[Brazilian Geek]

I get a lot of those but after studdering a bit at the begining of the chopped file but after a few seconds it plays smoothly.

I chopped an episode of the HHGttG a few weeks ago - I wanted to put the 'Share and Enjoy' song onto my MP3 player - and after locating the spot it started and for how long it played I dd'd it and presto - I passed it through mpg123 and it worked.

I guess it's just a matter of luck finding the correct spot to grab a header.

Not that easy (MP3 bit reservoir)

[Anonymous Coward]

MP3 has a "bit reservoir", meaning that MP3 frames are NOT independent of each other. Splitting it using only the headers (without understanding the MP3 data stream) may cause artifacts at the beginning or end of a clip. Most likely, you'll hear annoying static/pops at the beginning of the clip (often they're really loud, and may even damage speakers if the volume is up too loud).

If you're encoding MP3 files and intend to split them like this, try to disable the bit reservoir. If you use LAME, the --nores switch will disable it. This may degrade quality slightly, but if you're using VBR or ABR mode it won't really matter. Instead of "lame -b 128", use "lame --nores --abr 128" for example. Then you can split the MP3 without problems.

Splitting MP3's

[Animol]

Well, you could always just set up a Lego Mindstorms robot to open your case, remove a platter from a hard drive (assuming that's where they're stored) and physically operate a bandsaw to trim the media. There's no good way to reunite it but it's effective. If the songs are on a CD, just increase the laser's power to section off the track in question. I find physical separation of data makes for much better organization, if less practical use.