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/*
ogmmerge -- utility for splicing together ogg bitstreams
from component media subtypes
mp3_common.cpp
common routines for MP3 handling
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 "mp3_common.h"
#include "common.h"
int mp3_tabsel[2][16] =
{{0, 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320},
{0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160}};
long mp3_freqs[9] =
{44100, 48000, 32000, 22050, 24000, 16000, 11025, 12000, 8000};
int find_mp3_header(char *buf, int size, unsigned long *_header) {
int i;
unsigned long header;
int pos;
if (size < 4)
return -1;
for (pos = 0; pos <= (size - 4); pos++) {
for (i = 0, header = 0; i < 4; i++) {
header <<= 8;
header |= (unsigned char)buf[i + pos];
}
if ((header == FOURCC('R', 'I', 'F', 'F')) ||
((header & 0xffffff00) == FOURCC('I', 'D', '3', ' ')))
continue;
if ((header & 0xffe00000) != 0xffe00000)
continue;
if (!((header >> 17) & 3))
continue;
if (((header >> 12) & 0xf) == 0xf)
continue;
if (!((header >> 12) & 0xf))
continue;
if (((header >> 10) & 0x3) == 0x3)
continue;
if ((((header >> 19) & 1) == 1) && (((header >> 17) & 3) == 3) &&
(((header >> 16) & 1) == 1))
continue;
if ((header & 0xffff0000) == 0xfffe0000)
continue;
*_header = header;
return pos;
}
return -1;
}
void decode_mp3_header(unsigned long header, mp3_header_t *h) {
if (header & (1 << 20)) {
h->lsf = (header & (1 << 19)) ? 0 : 1;
h->mpeg25 = 0;
} else {
h->lsf = 1;
h->mpeg25 = 1;
}
h->mode = (header >> 6) & 3;
h->error_protection = ((header >> 16) & 1) ^ 1;
h->stereo = (h->mode == 3 ? 1 : 2);
if (h->lsf)
h->ssize = (h->stereo == 1 ? 9 : 17);
else
h->ssize = (h->stereo == 1 ? 17: 32);
if (h->error_protection)
h->ssize += 2;
h->bitrate_index = (header >> 12) & 15;
if (h->mpeg25)
h->sampling_frequency = 6 + ((header >> 10) & 3);
else
h->sampling_frequency = ((header >> 10) & 3) + (h->lsf * 3);
h->padding = (header >> 9) & 1;
h->framesize = (long)mp3_tabsel[h->lsf][h->bitrate_index] * 144000;
h->framesize /= (mp3_freqs[h->sampling_frequency] << h->lsf);
h->framesize = h->framesize + h->padding - 4;
}
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