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
0.08 October 21st 2003
Johan Vromans cought a glitch in asbin, which surfaced in 0.08 - now
fixed.
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 <
[email protected]>
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.
