dshow.cpp: fill in frame rate info (if demuxing)

modules/access/dshow/dshow.cpp

@@ -530,6 +530,8 @@ static int DemuxOpen( vlc_object_t *p_this )
                 fmt.video.i_gmask = 0x0000ff00;
                 fmt.video.i_rmask = 0x000000ff;
             }
+            fmt.video.i_frame_rate = 10000000000ULL/p_stream->header.video.AvgTimePerFrame;
+            fmt.video.i_frame_rate_base = 1000;
         }
         else if( p_stream->mt.majortype == MEDIATYPE_Audio )
         {