84 lines
1.7 KiB
C
Executable File
84 lines
1.7 KiB
C
Executable File
/*
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* Asterisk -- A telephony toolkit for Linux.
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*
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* MP3 Header Analysis Routines. Thanks to Robert Kaye for the logic!
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*
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* Copyright (C) 1999, Mark Spencer
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*
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* Mark Spencer <markster@linux-support.net>
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*
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* This program is free software, distributed under the terms of
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* the GNU General Public License
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*/
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static int bitrates1[] = { 0, 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320 };
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static int bitrates2[] = { 0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160 };
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static int samplerates1[] = { 44100, 48000, 32000 };
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static int samplerates2[] = { 22050, 24000, 16000 };
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static int outputsamples[] = { 576, 1152 };
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static int mp3_samples(unsigned char *header)
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{
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int ver = (header[1] & 0x8) >> 3;
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return outputsamples[ver];
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}
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static int mp3_bitrate(unsigned char *header)
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{
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int ver = (header[1] & 0x8) >> 3;
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int br = (header[2] >> 4);
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if (ver > 14) {
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ast_log(LOG_WARNING, "Invalid bit rate\n");
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return -1;
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}
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if (ver)
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return bitrates1[br];
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else {
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return bitrates2[br];
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}
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}
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static int mp3_samplerate(unsigned char *header)
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{
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int ver = (header[1] & 0x8) >> 3;
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int sr = (header[2] >> 2) & 0x3;
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if (ver > 2) {
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ast_log(LOG_WARNING, "Invalid sample rate\n");
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return -1;
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}
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if (ver)
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return samplerates1[sr];
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else
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return samplerates2[sr];
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}
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static int mp3_padding(unsigned char *header)
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{
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return (header[2] >> 1) & 0x1;
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}
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static int mp3_badheader(unsigned char *header)
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{
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if ((header[0] != 0xFF) || ((header[1] & 0xF0) != 0xF0))
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return -1;
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return 0;
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}
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static int mp3_framelen(unsigned char *header)
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{
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int br = mp3_bitrate(header);
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int sr = mp3_samplerate(header);
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int size;
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if ((br < 0) || (sr < 0))
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return -1;
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size = 144000 * br / sr + mp3_padding(header);
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return size;
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}
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