avcodec/nuv: prevent frame copying when outputting duplicate frames

Signed-off-by: NJames Almer <jamrial@gmail.com>

libavcodec/nuv.c

@@ -162,6 +162,7 @@ static int decode_frame(AVCodecContext *avctx, void *data, int *got_frame,
     int keyframe, ret;
     int size_change = 0;
     int minsize = 0;
+    int flags = 0;
     int result, init_frame = !avctx->frame_number;
     enum {
         NUV_UNCOMPRESSED  = '0',
@@ -204,6 +205,7 @@ static int decode_frame(AVCodecContext *avctx, void *data, int *got_frame,
         }
         break;
     case NUV_COPY_LAST:
+        flags |= FF_REGET_BUFFER_FLAG_READONLY;
         keyframe = 0;
         break;
     default:
@@ -268,7 +270,7 @@ retry:
         init_frame = 1;
     }
 
-    if ((result = ff_reget_buffer(avctx, c->pic, 0)) < 0)
+    if ((result = ff_reget_buffer(avctx, c->pic, flags)) < 0)
         return result;
     if (init_frame) {
         memset(c->pic->data[0], 0,    avctx->height * c->pic->linesize[0]);