diff options
Diffstat (limited to 'toolkit/components/mediasniffer/mp3sniff.c')
| -rw-r--r-- | toolkit/components/mediasniffer/mp3sniff.c | 156 |
1 files changed, 156 insertions, 0 deletions
diff --git a/toolkit/components/mediasniffer/mp3sniff.c b/toolkit/components/mediasniffer/mp3sniff.c new file mode 100644 index 000000000..a515d9c58 --- /dev/null +++ b/toolkit/components/mediasniffer/mp3sniff.c @@ -0,0 +1,156 @@ +/* This Source Code Form is subject to the terms of the Mozilla Public + * License, v. 2.0. If a copy of the MPL was not distributed with this file, + * You can obtain one at http://mozilla.org/MPL/2.0/. */ + +/* MPEG format parsing */ + +#include "mp3sniff.h" + +/* Maximum packet size is 320 kbits/s * 144 / 32 kHz + 1 padding byte */ +#define MP3_MAX_SIZE 1441 + +typedef struct { + int version; + int layer; + int errp; + int bitrate; + int freq; + int pad; + int priv; + int mode; + int modex; + int copyright; + int original; + int emphasis; +} mp3_header; + +/* Parse the 4-byte header in p and fill in the header struct. */ +static void mp3_parse(const uint8_t *p, mp3_header *header) +{ + const int bitrates[2][16] = { + /* MPEG version 1 layer 3 bitrates. */ + {0, 32000, 40000, 48000, 56000, 64000, 80000, 96000, + 112000, 128000, 160000, 192000, 224000, 256000, 320000, 0}, + /* MPEG Version 2 and 2.5 layer 3 bitrates */ + {0, 8000, 16000, 24000, 32000, 40000, 48000, 56000, 64000, + 80000, 96000, 112000, 128000, 144000, 160000, 0} }; + const int samplerates[4] = {44100, 48000, 32000, 0}; + + header->version = (p[1] & 0x18) >> 3; + header->layer = 4 - ((p[1] & 0x06) >> 1); + header->errp = (p[1] & 0x01); + + header->bitrate = bitrates[(header->version & 1) ? 0 : 1][(p[2] & 0xf0) >> 4]; + header->freq = samplerates[(p[2] & 0x0c) >> 2]; + if (header->version == 2) header->freq >>= 1; + else if (header->version == 0) header->freq >>= 2; + header->pad = (p[2] & 0x02) >> 1; + header->priv = (p[2] & 0x01); + + header->mode = (p[3] & 0xc0) >> 6; + header->modex = (p[3] & 0x30) >> 4; + header->copyright = (p[3] & 0x08) >> 3; + header->original = (p[3] & 0x04) >> 2; + header->emphasis = (p[3] & 0x03); +} + +/* calculate the size of an mp3 frame from its header */ +static int mp3_framesize(mp3_header *header) +{ + int size; + int scale; + + if ((header->version & 1) == 0) scale = 72; + else scale = 144; + size = header->bitrate * scale / header->freq; + if (header->pad) size += 1; + + return size; +} + +static int is_mp3(const uint8_t *p, long length) { + /* Do we have enough room to see a 4 byte header? */ + if (length < 4) return 0; + /* Do we have a sync pattern? */ + if (p[0] == 0xff && (p[1] & 0xe0) == 0xe0) { + /* Do we have any illegal field values? */ + if (((p[1] & 0x06) >> 1) == 0) return 0; /* No layer 4 */ + if (((p[2] & 0xf0) >> 4) == 15) return 0; /* Bitrate can't be 1111 */ + if (((p[2] & 0x0c) >> 2) == 3) return 0; /* Samplerate can't be 11 */ + /* Looks like a header. */ + if ((4 - ((p[1] & 0x06) >> 1)) != 3) return 0; /* Only want level 3 */ + return 1; + } + return 0; +} + +/* Identify an ID3 tag based on its header. */ +/* http://id3.org/id3v2.4.0-structure */ +static int is_id3(const uint8_t *p, long length) { + /* Do we have enough room to see the header? */ + if (length < 10) return 0; + /* Do we have a sync pattern? */ + if (p[0] == 'I' && p[1] == 'D' && p[2] == '3') { + if (p[3] == 0xff || p[4] == 0xff) return 0; /* Illegal version. */ + if (p[6] & 0x80 || p[7] & 0x80 || + p[8] & 0x80) return 0; /* Bad length encoding. */ + /* Looks like an id3 header. */ + return 1; + } + return 0; +} + +/* Calculate the size of an id3 tag structure from its header. */ +static int id3_framesize(const uint8_t *p, long length) +{ + int size; + + /* Header is 10 bytes. */ + if (length < 10) { + return 0; + } + /* Frame is header plus declared size. */ + size = 10 + (p[9] | (p[8] << 7) | (p[7] << 14) | (p[6] << 21)); + + return size; +} + +int mp3_sniff(const uint8_t *buf, long length) +{ + mp3_header header; + const uint8_t *p; + long skip; + long avail; + + p = buf; + avail = length; + while (avail >= 4) { + if (is_id3(p, avail)) { + /* Skip over any id3 tags */ + skip = id3_framesize(p, avail); + p += skip; + avail -= skip; + } else if (is_mp3(p, avail)) { + mp3_parse(p, &header); + skip = mp3_framesize(&header); + if (skip < 4 || skip + 4 >= avail) { + return 0; + } + p += skip; + avail -= skip; + /* Check for a second header at the expected offset. */ + if (is_mp3(p, avail)) { + /* Looks like mp3. */ + return 1; + } else { + /* No second header. Not mp3. */ + return 0; + } + } else { + /* No id3 tag or mp3 header. Not mp3. */ + return 0; + } + } + + return 0; +} |