avfilter/graphparser: remove 256 char limit from create_filter()

Fixes Ticket2803
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavfilter/graphparser.c

@@ -96,7 +96,7 @@ static int create_filter(AVFilterContext **filt_ctx, AVFilterGraph *ctx, int ind
 {
     AVFilter *filt;
     char inst_name[30];
-    char tmp_args[256];
+    char *tmp_args = NULL;
     int ret;
 
     snprintf(inst_name, sizeof(inst_name), "Parsed_%s_%d", filt_name, index);
@@ -118,8 +118,10 @@ static int create_filter(AVFilterContext **filt_ctx, AVFilterGraph *ctx, int ind
 
     if (!strcmp(filt_name, "scale") && args && !strstr(args, "flags") &&
         ctx->scale_sws_opts) {
-        snprintf(tmp_args, sizeof(tmp_args), "%s:%s",
+        tmp_args = av_asprintf("%s:%s",
                  args, ctx->scale_sws_opts);
+        if (!tmp_args)
+            return AVERROR(ENOMEM);
         args = tmp_args;
     }
 
@@ -130,10 +132,10 @@ static int create_filter(AVFilterContext **filt_ctx, AVFilterGraph *ctx, int ind
         if (args)
             av_log(log_ctx, AV_LOG_ERROR, " with args '%s'", args);
         av_log(log_ctx, AV_LOG_ERROR, "\n");
-        return ret;
     }
 
-    return 0;
+    av_free(tmp_args);
+    return ret;
 }
 
 /**