lavfi: search options on child objects.

The child objects must be allocated and inited in the
preinit() callback.

libavfilter/avfilter.c

@@ -897,7 +897,7 @@ static int process_options(AVFilterContext *ctx, AVDictionary **options,
             }
         } else {
         av_dict_set(options, key, value, 0);
-        if ((ret = av_opt_set(ctx->priv, key, value, 0)) < 0) {
+        if ((ret = av_opt_set(ctx->priv, key, value, AV_OPT_SEARCH_CHILDREN)) < 0) {
             if (!av_opt_find(ctx->priv, key, NULL, 0, AV_OPT_SEARCH_CHILDREN | AV_OPT_SEARCH_FAKE_OBJ)) {
             if (ret == AVERROR_OPTION_NOT_FOUND)
                 av_log(ctx, AV_LOG_ERROR, "Option '%s' not found\n", key);
@@ -948,7 +948,7 @@ int avfilter_init_dict(AVFilterContext *ctx, AVDictionary **options)
     }
 
     if (ctx->filter->priv_class) {
-        ret = av_opt_set_dict(ctx->priv, options);
+        ret = av_opt_set_dict2(ctx->priv, options, AV_OPT_SEARCH_CHILDREN);
         if (ret < 0) {
             av_log(ctx, AV_LOG_ERROR, "Error applying options to the filter.\n");
             return ret;