From gt6161c@PRISM.GATECH.EDUFri Jan 30 17:00:47 1998
Date: Wed, 28 Jan 1998 15:06:18 -0500
From: Chris Sidi <gt6161c@PRISM.GATECH.EDU>
Reply to: The mpg123 MPEG Audio Player <MPG123@TU-CLAUSTHAL.DE>,
    Chris Sidi <gt6161c@PRISM.GATECH.EDU>
To: MPG123@TU-CLAUSTHAL.DE
Subject: ASFv1 basic specs please... (fwd)

asfCDtomp3
==================
#!/usr/bin/perl -w

# asfCDtomp3 by Chris Sidi gt6161c@prism.gatech.edu
#
# Converts simple 128kbit mpeg layer 3 ASFs to plain mp3
#
# may not work if the file has index markers or wasn't created with
# wavtoasf.
#
# To write this program, I made mp3 WAVs in Sound Recorder and Cool
# Edit96, saving in ACM WAVeform mpeg layer 3. I them converted the
# WAVs to ASF with the netshow dos utility wavtoasf.  Using uthe unix
# utilities diff and bc I compared the ASFs to the original mp3 WAVs.
# I found there is about a 300-500 bytes header at the beginning of the
# ASF, followed by a mp3 header and mp3 data and then every 1000 bytes or
# so there's a 31 byte ASF header that you need to strip out.  If you
# have error correction turned on in wavtoasf then there's a little more
# asf data to strip out every 7 asf headers or so.
#
#
# If you use this code, please credit me and include this contact info:
# Chris Sidi gt6161c@prism.gatech.edu
# http://www.gatech.edu/wrek/wreknet.html
#
# If you improve this program (including getting it to work with other
# bitrates), or find out more about the ASFv1 spec (I've begged to microsoft
# for a description), please email me.  Also if you find out how to
# UDP or TCP stream an ASF, as I only know how to http stream from
# Netshow server (which isn't always supported).
#
#

##############################################################################
# Set to 1 if error correction is on.
##############################################################################

$asf_eccspan_flag = 0;

$asf_file = shift(@ARGV);

####################################################
# Settings for a 128kb/s 44.1khz stereo ASF file
####################################################

$mp3_header = pack("CCCC", 255, 251, 144, 68);
$mp3_frame_size = 416;
$asf_packet_size = 1699;
$asf_header_size =     (447 - $mp3_frame_size);
$asf_ecc_header_size = (2146 - $mp3_frame_size);

####################################################
# Settings for a 24kb/s 22,050hz mono ASF file
# uncomment this and comment the other settings to use.
####################################################
#
# $mp3_header = pack("CCCC", 255, 243, 48, 196);
# $mp3_frame_size = 77;
# $asf_packet_size = 577;
# $asf_header_size =     (108 - $mp3_frame_size);
# $asf_ecc_header_size = (685 - $mp3_frame_size);

##############################################################################

$asf_wavespan = 7;
$asf_packet_num_for_ecc = $asf_wavespan + 1;

$asf_ecc_bytes = $asf_ecc_header_size - $asf_header_size;
$asf_data_chunk_size = $asf_packet_size - $asf_header_size;

$tmp = "";
$buffer = "";

open(FILE, "$asf_file") || die "Can't open $asf_file: $!\n";

###############################################################################
# Get past ~500ish byte ASF header and to first mp3 header
# Print mp3 header
###############################################################################

while (1) {
	if (read(FILE, $tmp, 1)) {
		$buffer .= $tmp;

		if ( index($buffer, $mp3_header) > 300) {
			$first_mp3_header = index($buffer, $mp3_header);
			print STDERR "Found header at $first_mp3_header\n";

			read (FILE, $tmp, $asf_data_chunk_size - length($mp3_header));
			print STDOUT $mp3_header;
			print STDOUT $tmp;
			last;
		}
	}
	else {
		die "Never got to first header: $!\n";
	}
}

###############################################################################
# Strip ASF Headers (and Error correction if there)
# Print out mp3
###############################################################################

$asf_packet_num = 1;


while (read(FILE, $buffer, $asf_header_size)) {

	if ( $asf_eccspan_flag && (($asf_packet_num/$asf_packet_num_for_ecc) == int($asf_packet_num/$asf_packet_num_for_ecc)) ) {
		read(FILE, $buffer, $asf_ecc_bytes);

	}

 	read(FILE, $buffer, $asf_data_chunk_size);

	print STDOUT $buffer;

	$asf_packet_num++;
}