avformat/asfdec_f: Do not print errors if packets do not start with ECC

There is nothing wrong with such packets, the spec allows this
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/asfdec_f.c

@@ -113,6 +113,8 @@ typedef struct ASFContext {
 
     int no_resync_search;
     int export_xmp;
+
+    int uses_std_ecc;
 } ASFContext;
 
 static const AVOption options[] = {
@@ -956,6 +958,7 @@ static int asf_get_packet(AVFormatContext *s, AVIOContext *pb)
     int rsize = 8;
     int c, d, e, off;
 
+    if (asf->uses_std_ecc >= 0) {
         // if we do not know packet size, allow skipping up to 32 kB
         off = 32768;
         if (asf->no_resync_search)
@@ -972,6 +975,10 @@ static int asf_get_packet(AVFormatContext *s, AVIOContext *pb)
                 break;
         }
 
+        if (!asf->uses_std_ecc) {
+            asf->uses_std_ecc =  (c == 0x82 && !d && !e) ? 1 : -1;
+        }
+
         if (c != 0x82) {
             /* This code allows handling of -EAGAIN at packet boundaries (i.e.
             * if the packet sync code above triggers -EAGAIN). This does not
@@ -995,6 +1002,10 @@ static int asf_get_packet(AVFormatContext *s, AVIOContext *pb)
         } else if(!avio_feof(pb)) {
             avio_seek(pb, -1, SEEK_CUR); // FIXME
         }
+    } else {
+        c = avio_r8(pb);
+        d = avio_r8(pb);
+    }
 
     asf->packet_flags    = c;
     asf->packet_property = d;