typefind: Make the flac check more tight to not mistace some aac files for flac....

Add comments about the flac format. Tighten the check to not allow values that
refer to headers.

diff --git a/gst/typefind/gsttypefindfunctions.c b/gst/typefind/gsttypefindfunctions.c
index 8994f6e..cc5592a 100644 (file)
--- a/gst/typefind/gsttypefindfunctions.c
+++ b/gst/typefind/gsttypefindfunctions.c
@@ -567,14 +567,17 @@ flac_type_find (GstTypeFind * tf, gpointer unused)
     }
   }
 
-  /* flac without headers */
+  /* flac without headers (subset format) */
   /* 64K should be enough */
   while (c.offset < (64 * 1024)) {
     if (G_UNLIKELY (!data_scan_ctx_ensure_data (tf, &c, 4)))
       break;
 
+    /* look for frame header,
+     * http://flac.sourceforge.net/format.html#frame_header
+     */
     if (data[0] == 0xff && (data[1] >> 2) == 0x3e) {
-      /* bit 15 must be 0 */
+      /* bit 15 in the header must be 0 */
       if (((data[1] >> 1) & 0x01) == 0x01)
         goto advance;
 
@@ -585,19 +588,32 @@ flac_type_find (GstTypeFind * tf, gpointer unused)
       /* samplerate must be != 0x0f */
       if ((data[2] & 0x0f) == 0x0f)
         goto advance;
+      /* also 0 is invalid, as it means get the info from the header and we
+       * don't have headers if we are here */
+      if ((data[2] & 0x0f) == 0x00)
+        goto advance;
 
       /* channel assignment must be < 11 */
       if ((data[3] >> 4) >= 11)
         goto advance;
 
-      /* sample size must be != 0x07 */
+      /* sample size must be != 0x07 and != 0x05 */
       if (((data[3] >> 1) & 0x07) == 0x07)
         goto advance;
+      if (((data[3] >> 1) & 0x07) == 0x05)
+        goto advance;
+      /* also 0 is invalid, as it means get the info from the header and we
+       * don't have headers if we are here */
+      if (((data[3] >> 1) & 0x07) == 0x00)
+        goto advance;
 
       /* next bit must be 0 */
       if ((data[3] & 0x01) == 0x01)
         goto advance;
 
+      /* FIXME: shouldn't we include the crc check ? */
+
+      GST_DEBUG ("Found flac without headers at %d", (gint) c.offset);
       gst_type_find_suggest (tf, GST_TYPE_FIND_LIKELY, FLAC_CAPS);
       return;
     }
@@ -1149,7 +1165,8 @@ ac3_type_find (GstTypeFind * tf, gpointer unused)
 
 /* can only be detected by using the extension, in which case we use the default
  * GSM properties */
-static GstStaticCaps gsm_caps = GST_STATIC_CAPS ("audio/x-gsm, rate=8000, channels=1");
+static GstStaticCaps gsm_caps =
+GST_STATIC_CAPS ("audio/x-gsm, rate=8000, channels=1");
 
 #define GSM_CAPS (gst_static_caps_get(&gsm_caps))