NAME

MPEG::Audio::Frame - a class for weeding out MPEG audio frames out of a file handle.

SYNOPSIS

	use MPEG::Audio::Frame;

	open FILE,"file.mp3";

        while(my $frame = MPEG::Audio::Frame->read(\*FILE)){
		print $frame->offset(), ": ", $frame->bitrate(), "Kbps/", $frame->sample()/1000, "KHz\n"; # or something.
	}

DESCRIPTION

A very simple, pure Perl module which allows parsing out data from mp3 files, or streams, and chunking them up into different frames. You can use this to accurately determine the length of an mp3, filter nonaudio data, or chunk up the file for streaming via datagram. Virtually anything is possible.

METHODS

read GLOB

This is the constructor method. It receives a reference to a filehandle, and reads the next (hopefully) valid frame it can find on the stream. Please make sure use binmode if you're on a funny platform - the module doesn't know the difference, and shouldn't change stuff, IMHO.

asbin

Returns the binary data extracted from the handle. This is (definately|probably) a valid MPEG 1 or 2 audio frame.

asbin is also called via the overloaded operator "", so if you treat the frame object like a string, you'd get the binary data you'd get by calling asbin directly.

content

Returns the content of the frame, minus the header and the crc. This is (definately|probably) a valid MPEG 1 or 2 audio frame entity.

header

Returns a folded hash in list context, or a 4 byte long binary string in scalar context. The hash represents the header, split into it's parts, with bits translated into '0' and '1'. The binary string is (definately|probably) a valid MPEG 1 or 2 audio frame header.

crc

Returns the bytes of the checksum, as extracted from the handle. This is (definately) a valid checksum, unless there was none in the frame, in which case it will be undef. It (definately|probably) applies to the frame.

length

Returns the length, in bytes, of the entire frame. This is the length of the content, plus the four bytes of the header, and the two bytes of the crc, if applicable.

bitrate

Returns the bitrate in kilobits. Note that 128Kbps means 128000, and not 131072.

sample

Returns the sample rate in Hz.

seconds

Returns the length, in floating seconds, of the frame.

framerate

Should this frame describe the stream, the framerate would be the return value from this method.

broken

This returns true if the CRC computation failed for a protected layer I or III frame. It will always return false on unprotected frames.

pad

Wether or not the frame was padded.

offset

The offset where the frame was found in the handle, as reported by tell().

TIED HANDLE USAGE

You can also read frame objects via the <HANDLE> operator by tying a filehandle to this package in the following manner:

tie \*MP3, 'MPEG::Audio::Frame',\*FH;
while(<MP3>){
	print "frame at ", $_->offset(), "\n";
}

Way cool.

HISTORY

0.07 October 19th 2003

Made broken compute the CRC on demand instead of always.

Cryptographically signed distribution.

0.06 October 17th 2003

Fixed some doc errors, thanks to Nikolaus Schusser and Suleyman Gulsuner.

Fixed CRC computation on little endian machines.

0.05 August 3rd 2003

Added overloading of object to asbin by default.

Added real CRC checking for layers III and I (layer II is a longer story).

0.04 August 2nd 2003

Fixed the calculation of frame lengths when a CRC is present, thanks to Johan Vromans.

0.03 April 19th 2003

Reimplemented offset method, which came out of sync whilst working on various copies, thanks to Jeff Anderson.

0.02 April 18th 2003

Some minor documentation and distribution fixes were made.

AUTHOR

Yuval Kojman <nothingmuch@altern.org>

COPYRIGHT

Copyright (c) 2003 Yuval Kojman. All rights reserved
This program is free software; you can redistribute
it and/or modify it under the same terms as Perl itself.