toolkit/components/mediasniffer/mp3sniff.c@925c144e1f1f (annotated)
toolkit/components/mediasniffer/mp3sniff.c
Fri, 16 Jan 2015 18:13:44 +0100
- author
- Michael Schloh von Bennewitz <michael@schloh.com>
- date
- Fri, 16 Jan 2015 18:13:44 +0100
- branch
- TOR_BUG_9701
- changeset 14
- 925c144e1f1f
- permissions
- -rw-r--r--
Integrate suggestion from review to improve consistency with existing code.
| michael@0 | 1 | /* This Source Code Form is subject to the terms of the Mozilla Public |
| michael@0 | 2 | * License, v. 2.0. If a copy of the MPL was not distributed with this file, |
| michael@0 | 3 | * You can obtain one at http://mozilla.org/MPL/2.0/. */ |
| michael@0 | 4 | |
| michael@0 | 5 | /* MPEG format parsing */ |
| michael@0 | 6 | |
| michael@0 | 7 | #include "mp3sniff.h" |
| michael@0 | 8 | |
| michael@0 | 9 | /* Maximum packet size is 320 kbits/s * 144 / 32 kHz + 1 padding byte */ |
| michael@0 | 10 | #define MP3_MAX_SIZE 1441 |
| michael@0 | 11 | |
| michael@0 | 12 | typedef struct { |
| michael@0 | 13 | int version; |
| michael@0 | 14 | int layer; |
| michael@0 | 15 | int errp; |
| michael@0 | 16 | int bitrate; |
| michael@0 | 17 | int freq; |
| michael@0 | 18 | int pad; |
| michael@0 | 19 | int priv; |
| michael@0 | 20 | int mode; |
| michael@0 | 21 | int modex; |
| michael@0 | 22 | int copyright; |
| michael@0 | 23 | int original; |
| michael@0 | 24 | int emphasis; |
| michael@0 | 25 | } mp3_header; |
| michael@0 | 26 | |
| michael@0 | 27 | /* Parse the 4-byte header in p and fill in the header struct. */ |
| michael@0 | 28 | static void mp3_parse(const uint8_t *p, mp3_header *header) |
| michael@0 | 29 | { |
| michael@0 | 30 | const int bitrates[2][16] = { |
| michael@0 | 31 | /* MPEG version 1 layer 3 bitrates. */ |
| michael@0 | 32 | {0, 32000, 40000, 48000, 56000, 64000, 80000, 96000, |
| michael@0 | 33 | 112000, 128000, 160000, 192000, 224000, 256000, 320000, 0}, |
| michael@0 | 34 | /* MPEG Version 2 and 2.5 layer 3 bitrates */ |
| michael@0 | 35 | {0, 8000, 16000, 24000, 32000, 40000, 48000, 56000, 64000, |
| michael@0 | 36 | 80000, 96000, 112000, 128000, 144000, 160000, 0} }; |
| michael@0 | 37 | const int samplerates[4] = {44100, 48000, 32000, 0}; |
| michael@0 | 38 | |
| michael@0 | 39 | header->version = (p[1] & 0x18) >> 3; |
| michael@0 | 40 | header->layer = 4 - ((p[1] & 0x06) >> 1); |
| michael@0 | 41 | header->errp = (p[1] & 0x01); |
| michael@0 | 42 | |
| michael@0 | 43 | header->bitrate = bitrates[(header->version & 1) ? 0 : 1][(p[2] & 0xf0) >> 4]; |
| michael@0 | 44 | header->freq = samplerates[(p[2] & 0x0c) >> 2]; |
| michael@0 | 45 | if (header->version == 2) header->freq >>= 1; |
| michael@0 | 46 | else if (header->version == 0) header->freq >>= 2; |
| michael@0 | 47 | header->pad = (p[2] & 0x02) >> 1; |
| michael@0 | 48 | header->priv = (p[2] & 0x01); |
| michael@0 | 49 | |
| michael@0 | 50 | header->mode = (p[3] & 0xc0) >> 6; |
| michael@0 | 51 | header->modex = (p[3] & 0x30) >> 4; |
| michael@0 | 52 | header->copyright = (p[3] & 0x08) >> 3; |
| michael@0 | 53 | header->original = (p[3] & 0x04) >> 2; |
| michael@0 | 54 | header->emphasis = (p[3] & 0x03); |
| michael@0 | 55 | } |
| michael@0 | 56 | |
| michael@0 | 57 | /* calculate the size of an mp3 frame from its header */ |
| michael@0 | 58 | static int mp3_framesize(mp3_header *header) |
| michael@0 | 59 | { |
| michael@0 | 60 | int size; |
| michael@0 | 61 | int scale; |
| michael@0 | 62 | |
| michael@0 | 63 | if ((header->version & 1) == 0) scale = 72; |
| michael@0 | 64 | else scale = 144; |
| michael@0 | 65 | size = header->bitrate * scale / header->freq; |
| michael@0 | 66 | if (header->pad) size += 1; |
| michael@0 | 67 | |
| michael@0 | 68 | return size; |
| michael@0 | 69 | } |
| michael@0 | 70 | |
| michael@0 | 71 | static int is_mp3(const uint8_t *p, long length) { |
| michael@0 | 72 | /* Do we have enough room to see a 4 byte header? */ |
| michael@0 | 73 | if (length < 4) return 0; |
| michael@0 | 74 | /* Do we have a sync pattern? */ |
| michael@0 | 75 | if (p[0] == 0xff && (p[1] & 0xe0) == 0xe0) { |
| michael@0 | 76 | /* Do we have any illegal field values? */ |
| michael@0 | 77 | if (((p[1] & 0x06) >> 1) == 0) return 0; /* No layer 4 */ |
| michael@0 | 78 | if (((p[2] & 0xf0) >> 4) == 15) return 0; /* Bitrate can't be 1111 */ |
| michael@0 | 79 | if (((p[2] & 0x0c) >> 2) == 3) return 0; /* Samplerate can't be 11 */ |
| michael@0 | 80 | /* Looks like a header. */ |
| michael@0 | 81 | if ((4 - ((p[1] & 0x06) >> 1)) != 3) return 0; /* Only want level 3 */ |
| michael@0 | 82 | return 1; |
| michael@0 | 83 | } |
| michael@0 | 84 | return 0; |
| michael@0 | 85 | } |
| michael@0 | 86 | |
| michael@0 | 87 | /* Identify an ID3 tag based on its header. */ |
| michael@0 | 88 | /* http://id3.org/id3v2.4.0-structure */ |
| michael@0 | 89 | static int is_id3(const uint8_t *p, long length) { |
| michael@0 | 90 | /* Do we have enough room to see the header? */ |
| michael@0 | 91 | if (length < 10) return 0; |
| michael@0 | 92 | /* Do we have a sync pattern? */ |
| michael@0 | 93 | if (p[0] == 'I' && p[1] == 'D' && p[2] == '3') { |
| michael@0 | 94 | if (p[3] == 0xff || p[4] == 0xff) return 0; /* Illegal version. */ |
| michael@0 | 95 | if (p[6] & 0x80 || p[7] & 0x80 || |
| michael@0 | 96 | p[8] & 0x80) return 0; /* Bad length encoding. */ |
| michael@0 | 97 | /* Looks like an id3 header. */ |
| michael@0 | 98 | return 1; |
| michael@0 | 99 | } |
| michael@0 | 100 | return 0; |
| michael@0 | 101 | } |
| michael@0 | 102 | |
| michael@0 | 103 | /* Calculate the size of an id3 tag structure from its header. */ |
| michael@0 | 104 | static int id3_framesize(const uint8_t *p, long length) |
| michael@0 | 105 | { |
| michael@0 | 106 | int size; |
| michael@0 | 107 | |
| michael@0 | 108 | /* Header is 10 bytes. */ |
| michael@0 | 109 | if (length < 10) { |
| michael@0 | 110 | return 0; |
| michael@0 | 111 | } |
| michael@0 | 112 | /* Frame is header plus declared size. */ |
| michael@0 | 113 | size = 10 + (p[9] | (p[8] << 7) | (p[7] << 14) | (p[6] << 21)); |
| michael@0 | 114 | |
| michael@0 | 115 | return size; |
| michael@0 | 116 | } |
| michael@0 | 117 | |
| michael@0 | 118 | int mp3_sniff(const uint8_t *buf, long length) |
| michael@0 | 119 | { |
| michael@0 | 120 | mp3_header header; |
| michael@0 | 121 | const uint8_t *p, *q; |
| michael@0 | 122 | long skip; |
| michael@0 | 123 | long avail; |
| michael@0 | 124 | |
| michael@0 | 125 | p = buf; |
| michael@0 | 126 | q = p; |
| michael@0 | 127 | avail = length; |
| michael@0 | 128 | while (avail >= 4) { |
| michael@0 | 129 | if (is_id3(p, avail)) { |
| michael@0 | 130 | /* Skip over any id3 tags */ |
| michael@0 | 131 | skip = id3_framesize(p, avail); |
| michael@0 | 132 | p += skip; |
| michael@0 | 133 | avail -= skip; |
| michael@0 | 134 | } else if (is_mp3(p, avail)) { |
| michael@0 | 135 | mp3_parse(p, &header); |
| michael@0 | 136 | skip = mp3_framesize(&header); |
| michael@0 | 137 | if (skip < 4 || skip + 4 >= avail) { |
| michael@0 | 138 | return 0; |
| michael@0 | 139 | } |
| michael@0 | 140 | p += skip; |
| michael@0 | 141 | avail -= skip; |
| michael@0 | 142 | /* Check for a second header at the expected offset. */ |
| michael@0 | 143 | if (is_mp3(p, avail)) { |
| michael@0 | 144 | /* Looks like mp3. */ |
| michael@0 | 145 | return 1; |
| michael@0 | 146 | } else { |
| michael@0 | 147 | /* No second header. Not mp3. */ |
| michael@0 | 148 | return 0; |
| michael@0 | 149 | } |
| michael@0 | 150 | } else { |
| michael@0 | 151 | /* No id3 tag or mp3 header. Not mp3. */ |
| michael@0 | 152 | return 0; |
| michael@0 | 153 | } |
| michael@0 | 154 | } |
| michael@0 | 155 | |
| michael@0 | 156 | return 0; |
| michael@0 | 157 | } |
