328 lines
8.5 KiB
C
328 lines
8.5 KiB
C
/*____________________________________________________________________________
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FreeAmp - The Free MP3 Player
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MP3 Decoder originally Copyright (C) 1995-1997 Xing Technology
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Corp. http://www.xingtech.com
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Portions Copyright (C) 1998-1999 EMusic.com
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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$Id: mhead.c,v 1.7 1999/10/19 07:13:09 elrod Exp $
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____________________________________________________________________________*/
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/*------------ mhead.c ----------------------------------------------
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mpeg audio
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extract info from mpeg header
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portable version (adapted from c:\eco\mhead.c
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add Layer III
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mods 6/18/97 re mux restart, 32 bit ints
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mod 5/7/98 parse mpeg 2.5
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---------------------------------------------------------------------*/
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#include <stdlib.h>
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#include <stdio.h>
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#include <float.h>
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#include <math.h>
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#include "mhead.h" /* mpeg header structure */
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static const int mp_br_table[2][16] =
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{{0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160, 0},
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{0, 32, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320, 384, 0}};
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static const int mp_sr20_table[2][4] =
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{{441, 480, 320, -999}, {882, 960, 640, -999}};
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static const int mp_br_tableL1[2][16] =
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{{0, 32, 48, 56, 64, 80, 96, 112, 128, 144, 160, 176, 192, 224, 256, 0},/* mpeg2 */
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{0, 32, 64, 96, 128, 160, 192, 224, 256, 288, 320, 352, 384, 416, 448, 0}};
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static const int mp_br_tableL3[2][16] =
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{{0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160, 0}, /* mpeg 2 */
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{0, 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320, 0}};
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static int find_sync(unsigned char *buf, int n);
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static int sync_scan(unsigned char *buf, int n, int i0);
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static int sync_test(unsigned char *buf, int n, int isync, int padbytes);
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/*--------------------------------------------------------------*/
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int head_info(unsigned char *buf, unsigned int n, MPEG_HEAD * h)
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{
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int framebytes;
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int mpeg25_flag;
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if (n > 10000)
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n = 10000; /* limit scan for free format */
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h->sync = 0;
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//if ((buf[0] == 0xFF) && ((buf[1] & 0xF0) == 0xF0))
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if ((buf[0] == 0xFF) && ((buf[0+1] & 0xF0) == 0xF0))
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{
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mpeg25_flag = 0; // mpeg 1 & 2
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}
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else if ((buf[0] == 0xFF) && ((buf[0+1] & 0xF0) == 0xE0))
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{
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mpeg25_flag = 1; // mpeg 2.5
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}
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else
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return 0; // sync fail
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h->sync = 1;
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if (mpeg25_flag)
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h->sync = 2; //low bit clear signals mpeg25 (as in 0xFFE)
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h->id = (buf[0+1] & 0x08) >> 3;
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h->option = (buf[0+1] & 0x06) >> 1;
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h->prot = (buf[0+1] & 0x01);
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h->br_index = (buf[0+2] & 0xf0) >> 4;
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h->sr_index = (buf[0+2] & 0x0c) >> 2;
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h->pad = (buf[0+2] & 0x02) >> 1;
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h->private_bit = (buf[0+2] & 0x01);
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h->mode = (buf[0+3] & 0xc0) >> 6;
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h->mode_ext = (buf[0+3] & 0x30) >> 4;
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h->cr = (buf[0+3] & 0x08) >> 3;
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h->original = (buf[0+3] & 0x04) >> 2;
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h->emphasis = (buf[0+3] & 0x03);
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// if( mpeg25_flag ) {
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// if( h->sr_index == 2 ) return 0; // fail 8khz
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//}
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/* compute framebytes for Layer I, II, III */
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if (h->option < 1)
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return 0;
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if (h->option > 3)
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return 0;
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framebytes = 0;
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if (h->br_index > 0)
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{
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if (h->option == 3)
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{ /* layer I */
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framebytes =
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240 * mp_br_tableL1[h->id][h->br_index]
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/ mp_sr20_table[h->id][h->sr_index];
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framebytes = 4 * framebytes;
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}
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else if (h->option == 2)
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{ /* layer II */
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framebytes =
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2880 * mp_br_table[h->id][h->br_index]
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/ mp_sr20_table[h->id][h->sr_index];
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}
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else if (h->option == 1)
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{ /* layer III */
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if (h->id)
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{ // mpeg1
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framebytes =
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2880 * mp_br_tableL3[h->id][h->br_index]
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/ mp_sr20_table[h->id][h->sr_index];
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}
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else
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{ // mpeg2
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if (mpeg25_flag)
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{ // mpeg2.2
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framebytes =
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2880 * mp_br_tableL3[h->id][h->br_index]
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/ mp_sr20_table[h->id][h->sr_index];
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}
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else
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{
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framebytes =
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1440 * mp_br_tableL3[h->id][h->br_index]
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/ mp_sr20_table[h->id][h->sr_index];
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}
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}
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}
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}
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else
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framebytes = find_sync(buf, n); /* free format */
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return framebytes;
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}
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int head_info3(unsigned char *buf, unsigned int n, MPEG_HEAD *h, int *br, unsigned int *searchForward) {
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unsigned int pBuf = 0;
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// jdw insertion...
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while ((pBuf < n) && !((buf[pBuf] == 0xFF) &&
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((buf[pBuf+1] & 0xF0) == 0xF0 || (buf[pBuf+1] & 0xF0) == 0xE0)))
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{
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pBuf++;
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}
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if (pBuf == n) return 0;
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*searchForward = pBuf;
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return head_info2(&(buf[pBuf]),n,h,br);
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}
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/*--------------------------------------------------------------*/
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int head_info2(unsigned char *buf, unsigned int n, MPEG_HEAD * h, int *br)
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{
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int framebytes;
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/*--- return br (in bits/sec) in addition to frame bytes ---*/
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*br = 0;
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/*-- assume fail --*/
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framebytes = head_info(buf, n, h);
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if (framebytes == 0)
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return 0;
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switch (h->option)
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{
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case 1: /* layer III */
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{
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if (h->br_index > 0)
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*br = 1000 * mp_br_tableL3[h->id][h->br_index];
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else
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{
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if (h->id) // mpeg1
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*br = 1000 * framebytes * mp_sr20_table[h->id][h->sr_index] / (144 * 20);
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else
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{ // mpeg2
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if ((h->sync & 1) == 0) // flags mpeg25
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*br = 500 * framebytes * mp_sr20_table[h->id][h->sr_index] / (72 * 20);
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else
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*br = 1000 * framebytes * mp_sr20_table[h->id][h->sr_index] / (72 * 20);
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}
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}
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}
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break;
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case 2: /* layer II */
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{
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if (h->br_index > 0)
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*br = 1000 * mp_br_table[h->id][h->br_index];
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else
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*br = 1000 * framebytes * mp_sr20_table[h->id][h->sr_index] / (144 * 20);
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}
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break;
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case 3: /* layer I */
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{
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if (h->br_index > 0)
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*br = 1000 * mp_br_tableL1[h->id][h->br_index];
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else
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*br = 1000 * framebytes * mp_sr20_table[h->id][h->sr_index] / (48 * 20);
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}
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break;
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default:
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return 0; // fuck knows what this is, but it ain't one of ours...
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}
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return framebytes;
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}
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/*--------------------------------------------------------------*/
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static int compare(unsigned char *buf, unsigned char *buf2)
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{
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if (buf[0] != buf2[0])
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return 0;
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if (buf[1] != buf2[1])
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return 0;
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return 1;
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}
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/*----------------------------------------------------------*/
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/*-- does not scan for initial sync, initial sync assumed --*/
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static int find_sync(unsigned char *buf, int n)
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{
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int i0, isync, nmatch, pad;
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int padbytes, option;
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/* mod 4/12/95 i0 change from 72, allows as low as 8kbits for mpeg1 */
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i0 = 24;
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padbytes = 1;
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option = (buf[1] & 0x06) >> 1;
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if (option == 3)
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{
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padbytes = 4;
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i0 = 24; /* for shorter layer I frames */
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}
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pad = (buf[2] & 0x02) >> 1;
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n -= 3; /* need 3 bytes of header */
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while (i0 < 2000)
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{
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isync = sync_scan(buf, n, i0);
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i0 = isync + 1;
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isync -= pad;
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if (isync <= 0)
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return 0;
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nmatch = sync_test(buf, n, isync, padbytes);
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if (nmatch > 0)
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return isync;
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}
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return 0;
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}
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/*------------------------------------------------------*/
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/*---- scan for next sync, assume start is valid -------*/
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/*---- return number bytes to next sync ----------------*/
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static int sync_scan(unsigned char *buf, int n, int i0)
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{
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int i;
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for (i = i0; i < n; i++)
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if (compare(buf, buf + i))
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return i;
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return 0;
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}
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/*------------------------------------------------------*/
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/*- test consecutative syncs, input isync without pad --*/
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static int sync_test(unsigned char *buf, int n, int isync, int padbytes)
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{
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int i, nmatch, pad;
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nmatch = 0;
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for (i = 0;;)
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{
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pad = padbytes * ((buf[i + 2] & 0x02) >> 1);
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i += (pad + isync);
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if (i > n)
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break;
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if (!compare(buf, buf + i))
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return -nmatch;
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nmatch++;
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}
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return nmatch;
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}
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