Class ID3::Frame

class ID3::Frame

This class models ID3-Frames independent of the D3-version, e.g. 2.2.0, 2.3.0, 2.4.0 This module tries to hide all the ugly details about the Frame-internals and how to parse each Frame-type for each ID3-version.

The user doesn't need to use any of the methods provided by this module, but s/he can access the Instance Variables to examine each Frame.

Each Frame is organized as a "ordered Hash" , to preserve the order of it's fields, as they are defined by the ID3-standard

Because the names of the ID3-Frames vary between the ID3-versions, we are using a symbolic name to reference the Frame, not it's real (short) name.

Provided Functionality:

Reads and parses a frame upon initialization
Dumps a frame raw into a string
Low-level interface to ID3-Frames
Not all Frame-types are fully parsed, but can be accessed/copied/dumped as raw

Instance Variables:

name
version
raw
rawdata
rawheader
rawflags # if version is larger than 2.2.x
flags # Hash with the parsed flags, if version > 2.2.x
headerStartX
dataStartX

Instance Methods:

initialize # does all the hard work.. parses the Frame, defines parse/dump-methods
parse # defined during run-time, depending on the particular Frame-Type
dump # defined during run-time, depending on the particular Frame-Type

Examples:

	> require 'id3'
	=> true

	# here we're just creating an ID3::Tag2 object and read-in an mp3-file

	> t = ID3::Tag2.new
	=> {}
	> t.read("mp3/b.mp3")
	=> true
	> t.version
	=> "2.2.0"
	> t.keys
	=> ["ARTIST", "SONGLEN", "CONTENTTYPE", "ALBUM", "ENCODEDBY", "TRACKNUM", "TITLE", "YEAR", "PICTURE", "MEDIATYPE", "COMMENT"]

	# NOW let's look at the internals of a Frame:

	> t['ARTIST']
	=> {"encoding"=>0, "text"=>"Juno reactor"}

	> t['ARTIST'].keys
	=> ["encoding", "text"]

	> t['ARTIST'].order
	=> ["encoding", "text"]

	# PLEASE NOTE that the author does not have expertise with other than western character encodings..
	#             I'd like to hear some input how this can be implemented better..  and if/how Ruby can detect
	#             the character encoding of a string which was provided by the user

	> t['ARTIST']['text'] = "Juno Reactor"
	=> "Juno Reactor"

	> t['ARTIST'].raw
	=> "TP1\000\000\016\000Juno reactor\000"

	> t['ARTIST'].rawheader
	=> "TP1\000\000\016"

	> t['ARTIST'].rawdata
	=> "\000Juno reactor\000"

	# a lot of the really useful Frame types are text frames..

	> t['CONTENTTYPE']
	=> {"encoding"=>0, "text"=>"Electronica/Dance"}

	> t['YEAR']
	=> {"encoding"=>0, "text"=>"1997"}

	> t['SONGLEN']
	=> {"encoding"=>0, "text"=>"258847"}