lavfi/scale: enable runtime change flag

enable runtime change flag.
Signed-off-by: Jun Zhao <barryjzhao@tencent.com>

libavfilter/vf_scale.c

@@ -569,12 +569,13 @@ static const AVClass *child_class_next(const AVClass *prev)
 
 #define OFFSET(x) offsetof(ScaleContext, x)
 #define FLAGS AV_OPT_FLAG_VIDEO_PARAM|AV_OPT_FLAG_FILTERING_PARAM
+#define TFLAGS AV_OPT_FLAG_VIDEO_PARAM|AV_OPT_FLAG_FILTERING_PARAM|AV_OPT_FLAG_RUNTIME_PARAM
 
 static const AVOption scale_options[] = {
-    { "w",     "Output video width",          OFFSET(w_expr),    AV_OPT_TYPE_STRING,        .flags = FLAGS },
-    { "width", "Output video width",          OFFSET(w_expr),    AV_OPT_TYPE_STRING,        .flags = FLAGS },
-    { "h",     "Output video height",         OFFSET(h_expr),    AV_OPT_TYPE_STRING,        .flags = FLAGS },
-    { "height","Output video height",         OFFSET(h_expr),    AV_OPT_TYPE_STRING,        .flags = FLAGS },
+    { "w",     "Output video width",          OFFSET(w_expr),    AV_OPT_TYPE_STRING,        .flags = TFLAGS },
+    { "width", "Output video width",          OFFSET(w_expr),    AV_OPT_TYPE_STRING,        .flags = TFLAGS },
+    { "h",     "Output video height",         OFFSET(h_expr),    AV_OPT_TYPE_STRING,        .flags = TFLAGS },
+    { "height","Output video height",         OFFSET(h_expr),    AV_OPT_TYPE_STRING,        .flags = TFLAGS },
     { "flags", "Flags to pass to libswscale", OFFSET(flags_str), AV_OPT_TYPE_STRING, { .str = "bilinear" }, .flags = FLAGS },
     { "interl", "set interlacing", OFFSET(interlaced), AV_OPT_TYPE_BOOL, {.i64 = 0 }, -1, 1, FLAGS },
     { "size",   "set video size",          OFFSET(size_str), AV_OPT_TYPE_STRING, {.str = NULL}, 0, FLAGS },