nsv: Fix misdetection of MP3 files as NSV.

If an MP3 file contains the string NSVs, the NSV probe will confuse it for an
NSV file. Check for 0xBEEF after a Video/Audio chunk to achieve more accuracy.
Signed-off-by: Diego Biurrun <diego@biurrun.de>

libavformat/nsvdec.c

@@ -737,6 +737,9 @@ static int nsv_read_close(AVFormatContext *s)
 static int nsv_probe(AVProbeData *p)
 {
     int i;
+    int score;
+    int vsize, asize, auxcount;
+    score = 0;
     av_dlog(NULL, "nsv_probe(), buf_size %d\n", p->buf_size);
     /* check file header */
     /* streamed files might not have any header */
@@ -749,14 +752,25 @@ static int nsv_probe(AVProbeData *p)
     /* sometimes even the first header is at 9KB or something :^) */
     for (i = 1; i < p->buf_size - 3; i++) {
         if (p->buf[i+0] == 'N' && p->buf[i+1] == 'S' &&
-            p->buf[i+2] == 'V' && p->buf[i+3] == 's')
-            return AVPROBE_SCORE_MAX-20;
+            p->buf[i+2] == 'V' && p->buf[i+3] == 's') {
+            score = AVPROBE_SCORE_MAX/5;
+            /* Get the chunk size and check if at the end we are getting 0xBEEF */
+            auxcount = p->buf[i+19];
+            vsize = p->buf[i+20]  | p->buf[i+21] << 8;
+            asize = p->buf[i+22]  | p->buf[i+23] << 8;
+            vsize = (vsize << 4) | (auxcount >> 4);
+            if ((asize + vsize + i + 23) <  p->buf_size - 2) {
+                if (p->buf[i+23+asize+vsize+1] == 0xEF &&
+                    p->buf[i+23+asize+vsize+2] == 0xBE)
+                    return AVPROBE_SCORE_MAX-20;
+            }
+        }
     }
     /* so we'll have more luck on extension... */
     if (av_match_ext(p->filename, "nsv"))
         return AVPROBE_SCORE_MAX/2;
     /* FIXME: add mime-type check */
-    return 0;
+    return score;
 }
 
 AVInputFormat ff_nsv_demuxer = {