avformat/dv: about 3 times faster probe

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/dv.c

@@ -590,19 +590,21 @@ static int dv_probe(AVProbeData *p)
     if (p->buf_size < 5)
         return 0;
 
-    state = AV_RB32(p->buf);
-    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)
-            matches++;
-        state = (state << 8) | p->buf[i];
+    for (i = 0; i < p->buf_size-4; i++) {
+        unsigned state = AV_RB32(p->buf+i);
+        if ((state & 0x0007f840) == 0x00070000) {
+            // 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 & 0xffffff7f) == 0x1f07003f)
+                    matches++;
+            }
+            if (state == 0x003f0700 || state == 0xff3f0700)
+                marker_pos = i;
+            if (state == 0xff3f0701 && i - marker_pos == 80)
+                matches++;
+        }
     }
 
     if (matches && p->buf_size / matches < 1024 * 1024) {