videoparsers: set interlaced field in caps for mpeg2

https://bugzilla.gnome.org/show_bug.cgi?id=667218

gst/videoparsers/gstmpegvideoparse.c

@@ -673,6 +673,9 @@ gst_mpegv_parse_update_src_caps (GstMpegvParse * mpvparse)
       gst_caps_set_simple (caps, "level", G_TYPE_STRING, level, NULL);
     else
       GST_DEBUG_OBJECT (mpvparse, "Invalid level - %u", level_c);
+
+    gst_caps_set_simple (caps, "interlaced",
+        G_TYPE_BOOLEAN, !mpvparse->sequenceext.progressive, NULL);
   }
 
   gst_pad_set_caps (GST_BASE_PARSE_SRC_PAD (mpvparse), caps);