avfilter/vf_avgblur: add support for commands

doc/filters.texi

@@ -6211,6 +6211,13 @@ Set vertical radius size, if zero it will be same as @code{sizeX}.
 Default is @code{0}.
 @end table
 
+@subsection Commands
+This filter supports same commands as options.
+The command accepts the same syntax of the corresponding option.
+
+If the specified expression is not valid, it is kept at its current
+value.
+
 @section bbox
 
 Compute the bounding box for the non-black pixels in the input frame

libavfilter/vf_avgblur.c

@@ -287,6 +287,22 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *in)
     return ff_filter_frame(outlink, out);
 }
 
+static int process_command(AVFilterContext *ctx, const char *cmd, const char *args,
+                           char *res, int res_len, int flags)
+{
+    AverageBlurContext *s = ctx->priv;
+    int ret = 0;
+
+    if (   !strcmp(cmd, "sizeX") || !strcmp(cmd, "sizeY")
+        || !strcmp(cmd, "planes")) {
+        av_opt_set(s, cmd, args, 0);
+    } else {
+        ret = AVERROR(ENOSYS);
+    }
+
+    return ret;
+}
+
 static av_cold void uninit(AVFilterContext *ctx)
 {
     AverageBlurContext *s = ctx->priv;
@@ -322,4 +338,5 @@ AVFilter ff_vf_avgblur = {
     .inputs        = avgblur_inputs,
     .outputs       = avgblur_outputs,
     .flags         = AVFILTER_FLAG_SUPPORT_TIMELINE_GENERIC | AVFILTER_FLAG_SLICE_THREADS,
+    .process_command = process_command,
 };