From: Ruby Quiz <james@...>
Date: 2007-08-24T21:34:47+09:00
Subject: [QUIZ] ID3 Tags (#136)

The three rules of Ruby Quiz:

1.  Please do not post any solutions or spoiler discussion for this quiz until
48 hours have passed from the time on this message.

2.  Support Ruby Quiz by submitting ideas as often as you can:

http://www.rubyquiz.com/

3.  Enjoy!

Suggestion:  A [QUIZ] in the subject of emails about the problem helps everyone
on Ruby Talk follow the discussion.  Please reply to the original quiz message,
if you can.

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

The MP3 file format, didn't provide any means for including metadata about the
song.  ID3 tags were invented to solve this problem.

You can tell if an MP3 file includes ID3 tags by examining the last 128 bytes of
the file.  If they begin with the characters TAG, you have found an ID3 tag. 
The format of the tag is as follows:

	TAG song album artist comment year genre

The spaces above are just for us humans.  The actual tags are fixed-width fields
with no spacing between them.  Song, album, artist, and comment are 30 bytes
each.  The year is four bytes and the genre just gets one, which is an index
into a list of predefined genres I'll include at the end of this quiz.

A minor change was later made to ID3 tags to allow them to include track
numbers, creating ID3v1.1.  In that format, if the 29th byte of a comment is
null and the 30th is not, the 30th byte is an integer representing the track
number.

Later changes evolved ID3v2 which is a scary beast we won't worry about.

This week's Ruby Quiz is to write an ID3 tag parser.  Using a library is
cheating.  Roll up your sleeves and parse it yourself.  It's not hard at all.

If you don't have MP3 files to test your solution on, you can find some free
files at:

	http://www.mfiles.co.uk/mp3-files.htm

Here's the official genre list with some extensions added by Winamp:

	Blues
	Classic Rock
	Country
	Dance
	Disco
	Funk
	Grunge
	Hip-Hop
	Jazz
	Metal
	New Age
	Oldies
	Other
	Pop
	R&B
	Rap
	Reggae
	Rock
	Techno
	Industrial
	Alternative
	Ska
	Death Metal
	Pranks
	Soundtrack
	Euro-Techno
	Ambient
	Trip-Hop
	Vocal
	Jazz+Funk
	Fusion
	Trance
	Classical
	Instrumental
	Acid
	House
	Game
	Sound Clip
	Gospel
	Noise
	AlternRock
	Bass
	Soul
	Punk
	Space
	Meditative
	Instrumental Pop
	Instrumental Rock
	Ethnic
	Gothic
	Darkwave
	Techno-Industrial
	Electronic
	Pop-Folk
	Eurodance
	Dream
	Southern Rock
	Comedy
	Cult
	Gangsta
	Top 40
	Christian Rap
	Pop/Funk
	Jungle
	Native American
	Cabaret
	New Wave
	Psychadelic
	Rave
	Showtunes
	Trailer
	Lo-Fi
	Tribal
	Acid Punk
	Acid Jazz
	Polka
	Retro
	Musical
	Rock & Roll
	Hard Rock
	Folk
	Folk-Rock
	National Folk
	Swing
	Fast Fusion
	Bebob
	Latin
	Revival
	Celtic
	Bluegrass
	Avantgarde
	Gothic Rock
	Progressive Rock
	Psychedelic Rock
	Symphonic Rock
	Slow Rock
	Big Band
	Chorus
	Easy Listening
	Acoustic
	Humour
	Speech
	Chanson
	Opera
	Chamber Music
	Sonata
	Symphony
	Booty Bass
	Primus
	Porn Groove
	Satire
	Slow Jam
	Club
	Tango
	Samba
	Folklore
	Ballad
	Power Ballad
	Rhythmic Soul
	Freestyle
	Duet
	Punk Rock
	Drum Solo
	A capella
	Euro-House
	Dance Hall