1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/toolkit/components/mediasniffer/mp3sniff.c Wed Dec 31 06:09:35 2014 +0100
1.3 @@ -0,0 +1,157 @@
1.4 +/* This Source Code Form is subject to the terms of the Mozilla Public
1.5 + * License, v. 2.0. If a copy of the MPL was not distributed with this file,
1.6 + * You can obtain one at http://mozilla.org/MPL/2.0/. */
1.7 +
1.8 +/* MPEG format parsing */
1.9 +
1.10 +#include "mp3sniff.h"
1.11 +
1.12 +/* Maximum packet size is 320 kbits/s * 144 / 32 kHz + 1 padding byte */
1.13 +#define MP3_MAX_SIZE 1441
1.14 +
1.15 +typedef struct {
1.16 + int version;
1.17 + int layer;
1.18 + int errp;
1.19 + int bitrate;
1.20 + int freq;
1.21 + int pad;
1.22 + int priv;
1.23 + int mode;
1.24 + int modex;
1.25 + int copyright;
1.26 + int original;
1.27 + int emphasis;
1.28 +} mp3_header;
1.29 +
1.30 +/* Parse the 4-byte header in p and fill in the header struct. */
1.31 +static void mp3_parse(const uint8_t *p, mp3_header *header)
1.32 +{
1.33 + const int bitrates[2][16] = {
1.34 + /* MPEG version 1 layer 3 bitrates. */
1.35 + {0, 32000, 40000, 48000, 56000, 64000, 80000, 96000,
1.36 + 112000, 128000, 160000, 192000, 224000, 256000, 320000, 0},
1.37 + /* MPEG Version 2 and 2.5 layer 3 bitrates */
1.38 + {0, 8000, 16000, 24000, 32000, 40000, 48000, 56000, 64000,
1.39 + 80000, 96000, 112000, 128000, 144000, 160000, 0} };
1.40 + const int samplerates[4] = {44100, 48000, 32000, 0};
1.41 +
1.42 + header->version = (p[1] & 0x18) >> 3;
1.43 + header->layer = 4 - ((p[1] & 0x06) >> 1);
1.44 + header->errp = (p[1] & 0x01);
1.45 +
1.46 + header->bitrate = bitrates[(header->version & 1) ? 0 : 1][(p[2] & 0xf0) >> 4];
1.47 + header->freq = samplerates[(p[2] & 0x0c) >> 2];
1.48 + if (header->version == 2) header->freq >>= 1;
1.49 + else if (header->version == 0) header->freq >>= 2;
1.50 + header->pad = (p[2] & 0x02) >> 1;
1.51 + header->priv = (p[2] & 0x01);
1.52 +
1.53 + header->mode = (p[3] & 0xc0) >> 6;
1.54 + header->modex = (p[3] & 0x30) >> 4;
1.55 + header->copyright = (p[3] & 0x08) >> 3;
1.56 + header->original = (p[3] & 0x04) >> 2;
1.57 + header->emphasis = (p[3] & 0x03);
1.58 +}
1.59 +
1.60 +/* calculate the size of an mp3 frame from its header */
1.61 +static int mp3_framesize(mp3_header *header)
1.62 +{
1.63 + int size;
1.64 + int scale;
1.65 +
1.66 + if ((header->version & 1) == 0) scale = 72;
1.67 + else scale = 144;
1.68 + size = header->bitrate * scale / header->freq;
1.69 + if (header->pad) size += 1;
1.70 +
1.71 + return size;
1.72 +}
1.73 +
1.74 +static int is_mp3(const uint8_t *p, long length) {
1.75 + /* Do we have enough room to see a 4 byte header? */
1.76 + if (length < 4) return 0;
1.77 + /* Do we have a sync pattern? */
1.78 + if (p[0] == 0xff && (p[1] & 0xe0) == 0xe0) {
1.79 + /* Do we have any illegal field values? */
1.80 + if (((p[1] & 0x06) >> 1) == 0) return 0; /* No layer 4 */
1.81 + if (((p[2] & 0xf0) >> 4) == 15) return 0; /* Bitrate can't be 1111 */
1.82 + if (((p[2] & 0x0c) >> 2) == 3) return 0; /* Samplerate can't be 11 */
1.83 + /* Looks like a header. */
1.84 + if ((4 - ((p[1] & 0x06) >> 1)) != 3) return 0; /* Only want level 3 */
1.85 + return 1;
1.86 + }
1.87 + return 0;
1.88 +}
1.89 +
1.90 +/* Identify an ID3 tag based on its header. */
1.91 +/* http://id3.org/id3v2.4.0-structure */
1.92 +static int is_id3(const uint8_t *p, long length) {
1.93 + /* Do we have enough room to see the header? */
1.94 + if (length < 10) return 0;
1.95 + /* Do we have a sync pattern? */
1.96 + if (p[0] == 'I' && p[1] == 'D' && p[2] == '3') {
1.97 + if (p[3] == 0xff || p[4] == 0xff) return 0; /* Illegal version. */
1.98 + if (p[6] & 0x80 || p[7] & 0x80 ||
1.99 + p[8] & 0x80) return 0; /* Bad length encoding. */
1.100 + /* Looks like an id3 header. */
1.101 + return 1;
1.102 + }
1.103 + return 0;
1.104 +}
1.105 +
1.106 +/* Calculate the size of an id3 tag structure from its header. */
1.107 +static int id3_framesize(const uint8_t *p, long length)
1.108 +{
1.109 + int size;
1.110 +
1.111 + /* Header is 10 bytes. */
1.112 + if (length < 10) {
1.113 + return 0;
1.114 + }
1.115 + /* Frame is header plus declared size. */
1.116 + size = 10 + (p[9] | (p[8] << 7) | (p[7] << 14) | (p[6] << 21));
1.117 +
1.118 + return size;
1.119 +}
1.120 +
1.121 +int mp3_sniff(const uint8_t *buf, long length)
1.122 +{
1.123 + mp3_header header;
1.124 + const uint8_t *p, *q;
1.125 + long skip;
1.126 + long avail;
1.127 +
1.128 + p = buf;
1.129 + q = p;
1.130 + avail = length;
1.131 + while (avail >= 4) {
1.132 + if (is_id3(p, avail)) {
1.133 + /* Skip over any id3 tags */
1.134 + skip = id3_framesize(p, avail);
1.135 + p += skip;
1.136 + avail -= skip;
1.137 + } else if (is_mp3(p, avail)) {
1.138 + mp3_parse(p, &header);
1.139 + skip = mp3_framesize(&header);
1.140 + if (skip < 4 || skip + 4 >= avail) {
1.141 + return 0;
1.142 + }
1.143 + p += skip;
1.144 + avail -= skip;
1.145 + /* Check for a second header at the expected offset. */
1.146 + if (is_mp3(p, avail)) {
1.147 + /* Looks like mp3. */
1.148 + return 1;
1.149 + } else {
1.150 + /* No second header. Not mp3. */
1.151 + return 0;
1.152 + }
1.153 + } else {
1.154 + /* No id3 tag or mp3 header. Not mp3. */
1.155 + return 0;
1.156 + }
1.157 + }
1.158 +
1.159 + return 0;
1.160 +}
