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 0000000000..cb1e2fdc1d
--- /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;
+}