avfilter/vf_threshold: add support for commands

doc/filters.texi

@@ -19863,6 +19863,10 @@ otherwise fourth stream pixel component value will be picked.
 
 Using color source filter one can perform various types of thresholding:
 
+@subsection Commands
+
+This filter supports the all options as @ref{commands}.
+
 @subsection Examples
 
 @itemize

libavfilter/vf_threshold.c

@@ -34,7 +34,7 @@
 #include "threshold.h"
 
 #define OFFSET(x) offsetof(ThresholdContext, x)
-#define FLAGS AV_OPT_FLAG_VIDEO_PARAM|AV_OPT_FLAG_FILTERING_PARAM
+#define FLAGS AV_OPT_FLAG_VIDEO_PARAM|AV_OPT_FLAG_FILTERING_PARAM|AV_OPT_FLAG_RUNTIME_PARAM
 
 static const AVOption threshold_options[] = {
     { "planes", "set planes to filter", OFFSET(planes), AV_OPT_TYPE_INT,  {.i64=15}, 0, 15, FLAGS},
@@ -365,4 +365,5 @@ const AVFilter ff_vf_threshold = {
     .inputs        = inputs,
     .outputs       = outputs,
     .flags         = AVFILTER_FLAG_SUPPORT_TIMELINE_INTERNAL | AVFILTER_FLAG_SLICE_THREADS,
+    .process_command = ff_filter_process_command,
 };