[FFmpeg-devel] [PATCH] another stab at improved dv probe

[Maksym Veremeyenko]

Reimar D?ffinger ???????(??):
> Hello,
> another attempt at dv probe. It is still on the simple side, checking
> that the distance between the section header difs is exactly 12000 bytes
> or also checking the video header difs etc. is possible, but currently I
> am still going for "as stupid as I can get away with".
May i propose one more improvement to your patch that check if headers 
starts in position odd to 12000 that cause to rise ratio:

Index: dv.c
===================================================================
--- dv.c	(revision 19970)
+++ dv.c	(working copy)
@@ -489,6 +489,8 @@
      unsigned state, marker_pos = 0;
      int i;
      int matches = 0;
+    int secondary_matches = 0;
+    int primary_matches = 0;

      if (p->buf_size < 5)
          return 0;
@@ -497,6 +499,12 @@
      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++;
+            primary_matches += (i - 4) % 12000;
+        }
          if (state == 0x003f0700 || state == 0xff3f0700)
              marker_pos = i;
          if (state == 0xff3f0701 && i - marker_pos == 80)
@@ -505,8 +513,11 @@
      }

      if (matches && p->buf_size / matches < 1024*1024) {
-        if (matches > 4)
-            return AVPROBE_SCORE_MAX*3/4; // not max to avoid dv in mov 
to match
+        if (matches > 4 || (secondary_matches >= 10 && p->buf_size / 
secondary_matches < 24000)) {
+            if(!primary_matches)
+                return AVPROBE_SCORE_MAX - 1;
+            return AVPROBE_SCORE_MAX / 2;
+        }
          return AVPROBE_SCORE_MAX/4;
      }
      return 0;

i had a mov file where DV frames chunk start from 17-th byte and probe 
test found that its a raw DV stream with ratio 0.75. In that case 
truncated raw DV stream will have 0.5 but normal 0.99

-- 
________________________________________
Maksym Veremeyenko