This gem isn’t originally mine, but i’ve added things etc…

The gem can now be used with bundler and by extension, Rails 3, just use…

gem “mp4info”, :git => “git://github.com/arbarlow/ruby-mp4info.git”, :require => “mp4info”

MP4Info supports the reading of tags and file info from MP4 audio files. It is based on the Perl module MP4::Info (search.cpan.org/~jhar/MP4-Info/) Note: MP4Info does not currently support Unicode strings.

This program is free software; you can redistribute it and/or modify it under the terms of version 2 of the GNU General Public License as published by the Free Software Foundation.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA

With mp4info.rb in your load path, do:

require 'mp4info'

Once the library is loaded, an MP4Info object is created by sending an IO object to MP4Info#new. MP4Info also provides the MP4Info#open method, which takes String containing a filename.

file = "my_favorite_song.mp4"
info = MP4Info.open(file)

io_stream = File.new("that_other_song.m4a")
other_info = MP4Info.new(io_stream)

Once an MP4Info object is succesfully created, a number of tags are avalible:

* ALB   - Album
* APID  - Apple Store ID
* ART   - Artist
* CMT   - Comment
* COVR  - Album art (typically jpeg data)
* CPIL  - Compilation (boolean)
* CPRT  - Copyright statement
* DAY   - Year
* DISK  - Disk number & total (Array of two integers)
* GNRE  - Genre
* GRP   - Grouping
* NAM   - Title
* RTNG  - Rating (integer)
* TMPO  - Tempo (integer)
* TOO   - Encoder
* TRKN  - Track number & total (Array of two integers)
* WRT   - Author or composer

The following extra information about the audio file is also provided:

* VERSION   - MPEG version (=4)
* LAYER     - Doesn't really mean antyhing, but here in case we need it
              for compatibility with an MP3 library...
* BITRATE   - Bitrate in kbps (average for VBR files)
              The formula used to generate this seems a little suspect.
* FREQUENCY - Frequency in kHz
* SIZE      - Bytes in audio stream

* SECS  - Total seconds, rounded to nearest second
* MM    - Minutes
* SS    - Leftover seconds
* MS    - Leftover milliseconds, rounded to nearest millisecond
* TIME  - Time in MM:SS, rounded to nearest second

* COPYRIGHT	- Non-nil if audio is copyrighted
* ENCRYPTED	- Non-nil if audio data is encrypted