lavfi/streamselect: enable runtime change flag

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

libavfilter/f_streamselect.c

@@ -41,9 +41,10 @@ typedef struct StreamSelectContext {
 
 #define OFFSET(x) offsetof(StreamSelectContext, x)
 #define FLAGS AV_OPT_FLAG_VIDEO_PARAM | AV_OPT_FLAG_AUDIO_PARAM | AV_OPT_FLAG_FILTERING_PARAM
+#define TFLAGS AV_OPT_FLAG_VIDEO_PARAM | AV_OPT_FLAG_AUDIO_PARAM | AV_OPT_FLAG_FILTERING_PARAM | AV_OPT_FLAG_RUNTIME_PARAM
 static const AVOption streamselect_options[] = {
     { "inputs",  "number of input streams",           OFFSET(nb_inputs),  AV_OPT_TYPE_INT,    {.i64=2},    2, INT_MAX,  .flags=FLAGS },
-    { "map",     "input indexes to remap to outputs", OFFSET(map_str),    AV_OPT_TYPE_STRING, {.str=NULL},              .flags=FLAGS },
+    { "map",     "input indexes to remap to outputs", OFFSET(map_str),    AV_OPT_TYPE_STRING, {.str=NULL},              .flags=TFLAGS },
     { NULL }
 };