avfilter/vignette: add direct rendering.

libavfilter/vf_vignette.c

@@ -197,18 +197,23 @@ static inline double get_dither_value(VignetteContext *s)
 
 static int filter_frame(AVFilterLink *inlink, AVFrame *in)
 {
-    unsigned x, y;
+    unsigned x, y, direct = 0;
     AVFilterContext *ctx = inlink->dst;
     VignetteContext *s = ctx->priv;
     AVFilterLink *outlink = ctx->outputs[0];
     AVFrame *out;
 
+    if (av_frame_is_writable(in)) {
+        direct = 1;
+        out = in;
+    } else {
     out = ff_get_video_buffer(outlink, outlink->w, outlink->h);
     if (!out) {
         av_frame_free(&in);
         return AVERROR(ENOMEM);
     }
     av_frame_copy_props(out, in);
+    }
 
     if (s->eval_mode == EVAL_MODE_FRAME)
         update_context(s, inlink, in);
@@ -268,7 +273,8 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *in)
         }
     }
 
-    av_frame_free(&in);
+    if (!direct)
+        av_frame_free(&in);
     return ff_filter_frame(outlink, out);
 }