theoradec: Set telemetry options only if they are nonzero

Setting telemetry options, even to zero, causes libtheora to enable an expensive code path. For large enough videos (e.g. 1920x1080) this can increase the time to decode each frame by 30-40 ms, which can be enough to cause noticeable stutter.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-base/-/merge_requests/892>

ext/theora/gsttheoradec.c

@@ -471,19 +471,23 @@ theora_handle_type_packet (GstTheoraDec * dec)
   /* done */
   dec->decoder = th_decode_alloc (&dec->info, dec->setup);
 
-  if (th_decode_ctl (dec->decoder, TH_DECCTL_SET_TELEMETRY_MV,
+  if (dec->telemetry_mv &&
+      th_decode_ctl (dec->decoder, TH_DECCTL_SET_TELEMETRY_MV,
           &dec->telemetry_mv, sizeof (dec->telemetry_mv)) != TH_EIMPL) {
     GST_WARNING_OBJECT (dec, "Could not enable MV visualisation");
   }
-  if (th_decode_ctl (dec->decoder, TH_DECCTL_SET_TELEMETRY_MBMODE,
+  if (dec->telemetry_mbmode &&
+      th_decode_ctl (dec->decoder, TH_DECCTL_SET_TELEMETRY_MBMODE,
           &dec->telemetry_mbmode, sizeof (dec->telemetry_mbmode)) != TH_EIMPL) {
     GST_WARNING_OBJECT (dec, "Could not enable MB mode visualisation");
   }
-  if (th_decode_ctl (dec->decoder, TH_DECCTL_SET_TELEMETRY_QI,
+  if (dec->telemetry_qi &&
+      th_decode_ctl (dec->decoder, TH_DECCTL_SET_TELEMETRY_QI,
           &dec->telemetry_qi, sizeof (dec->telemetry_qi)) != TH_EIMPL) {
     GST_WARNING_OBJECT (dec, "Could not enable QI mode visualisation");
   }
-  if (th_decode_ctl (dec->decoder, TH_DECCTL_SET_TELEMETRY_BITS,
+  if (dec->telemetry_bits &&
+      th_decode_ctl (dec->decoder, TH_DECCTL_SET_TELEMETRY_BITS,
           &dec->telemetry_bits, sizeof (dec->telemetry_bits)) != TH_EIMPL) {
     GST_WARNING_OBJECT (dec, "Could not enable BITS mode visualisation");
   }