Extend DV autodetection to also reliably detect single-frame DVs with

a higher score that MAX/4.
It checks that there are at least 10 DIF headers and at least one per
24000 bytes, and if so considers the file reliably detected as DV.
Passes probetest, too.


git-svn-id: file:///var/local/repositories/ffmpeg/trunk@20074 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavformat/dv.c

@@ -489,6 +489,7 @@ static int dv_probe(AVProbeData *p)
     unsigned state, marker_pos = 0;
     int i;
     int matches = 0;
+    int secondary_matches = 0;
 
     if (p->buf_size < 5)
         return 0;
@@ -497,6 +498,10 @@ static int dv_probe(AVProbeData *p)
     for (i = 4; i < p->buf_size; i++) {
         if ((state & 0xffffff7f) == 0x1f07003f)
             matches++;
+        // any section header, also with seq/chan num != 0,
+        // should appear around every 12000 bytes, at least 10 per frame
+        if ((state & 0xff07ff7f) == 0x1f07003f)
+            secondary_matches++;
         if (state == 0x003f0700 || state == 0xff3f0700)
             marker_pos = i;
         if (state == 0xff3f0701 && i - marker_pos == 80)
@@ -505,7 +510,7 @@ static int dv_probe(AVProbeData *p)
     }
 
     if (matches && p->buf_size / matches < 1024*1024) {
-        if (matches > 4)
+        if (matches > 4 || (secondary_matches >= 10 && p->buf_size / secondary_matches < 24000))
             return AVPROBE_SCORE_MAX*3/4; // not max to avoid dv in mov to match
         return AVPROBE_SCORE_MAX/4;
     }