mkvtoolnix/ac3_common.cpp
2003-02-16 12:11:31 +00:00

96 lines
2.5 KiB
C++

/*
ogmmerge -- utility for splicing together ogg bitstreams
from component media subtypes
ac3common.c
AC3 common functions
Written by Moritz Bunkus <moritz@bunkus.org>
Based on Xiph.org's 'oggmerge' found in their CVS repository
See http://www.xiph.org
Distributed under the GPL
see the file COPYING for details
or visit http://www.gnu.org/copyleft/gpl.html
*/
#include <malloc.h>
#include <string.h>
#include "ac3_common.h"
int find_ac3_header(unsigned char *buf, int size, ac3_header_t *ac3_header) {
static int rate[] = { 32, 40, 48, 56, 64, 80, 96, 112, 128, 160,
192, 224, 256, 320, 384, 448, 512, 576, 640};
static unsigned char lfeon[8] = {0x10, 0x10, 0x04, 0x04, 0x04, 0x01,
0x04, 0x01};
static unsigned char halfrate[12] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 2, 3};
ac3_header_t header;
int i;
int frmsizecod;
int bitrate;
int half;
int acmod;
for (i = 0; i < (size - 7); i++) {
if ((buf[i] != 0x0b) || (buf[i + 1] != 0x77))
continue;
if (buf[i + 5] >= 0x60)
continue;
half = halfrate[buf[i + 5] >> 3];
acmod = buf[i + 6] >> 5;
header.flags = ((((buf[i + 6] & 0xf8) == 0x50) ? A52_DOLBY : acmod) |
((buf[i + 6] & lfeon[acmod]) ? A52_LFE : 0));
frmsizecod = buf[i + 4] & 63;
if (frmsizecod >= 38)
return -1;
bitrate = rate[frmsizecod >> 1];
header.bit_rate = (bitrate * 1000) >> half;
switch (buf[i + 4] & 0xc0) {
case 0:
header.sample_rate = 48000 >> half;
header.bytes = 4 * bitrate;
break;
case 0x40:
header.sample_rate = 44100 >> half;
header.bytes = 2 * (320 * bitrate / 147 + (frmsizecod & 1));
break;
case 0x80:
header.sample_rate = 32000 >> half;
header.bytes = 6 * bitrate;
break;
default:
return -1;
}
switch(header.flags & A52_CHANNEL_MASK) {
case A52_MONO:
header.channels=1;
break;
case A52_CHANNEL:
case A52_STEREO:
case A52_CHANNEL1:
case A52_CHANNEL2:
case A52_DOLBY:
header.channels=2;
break;
case A52_2F1R:
case A52_3F:
header.channels=3;
break;
case A52_3F1R:
case A52_2F2R:
header.channels=4;
break;
case A52_3F2R:
header.channels=5;
break;
}
if (header.flags & A52_LFE)
header.channels++;
memcpy(ac3_header, &header, sizeof(ac3_header_t));
return i;
}
return -1;
}