avformat/dss: set packet duration

Value taken from the decoder implementation
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/dss.c

@@ -228,7 +228,7 @@ static int dss_sp_read_packet(AVFormatContext *s, AVPacket *pkt)
     if (ret < 0)
         return ret;
 
-    pkt->duration     = 0;
+    pkt->duration     = 264;
     pkt->pos = pos;
     pkt->stream_index = 0;