avformat/mxfdec: optimize probing

about 71 times faster
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/mxfdec.c

@@ -47,6 +47,7 @@
 #include "libavutil/avassert.h"
 #include "libavutil/mathematics.h"
 #include "libavcodec/bytestream.h"
+#include "libavutil/intreadwrite.h"
 #include "libavutil/timecode.h"
 #include "avformat.h"
 #include "internal.h"
@@ -2456,10 +2457,19 @@ static int mxf_probe(AVProbeData *p) {
 
     /* Must skip Run-In Sequence and search for MXF header partition pack key SMPTE 377M 5.5 */
     end -= sizeof(mxf_header_partition_pack_key);
-    for (; bufp < end; bufp++) {
-        if (IS_KLV_KEY(bufp, mxf_header_partition_pack_key))
-            return AVPROBE_SCORE_MAX;
+
+    for (; bufp < end;) {
+        if (!((bufp[13] - 1) & 0xF2)){
+            if (AV_RN32(bufp   ) == AV_RN32(mxf_header_partition_pack_key   ) &&
+                AV_RN32(bufp+ 4) == AV_RN32(mxf_header_partition_pack_key+ 4) &&
+                AV_RN32(bufp+ 8) == AV_RN32(mxf_header_partition_pack_key+ 8) &&
+                AV_RN16(bufp+12) == AV_RN16(mxf_header_partition_pack_key+12))
+                return AVPROBE_SCORE_MAX;
+            bufp ++;
+        } else
+            bufp += 10;
     }
+
     return 0;
 }