avcodec/snow: only allocate space for edges when encoding

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

libavcodec/snow.c

@@ -69,11 +69,17 @@ void ff_snow_inner_add_yblock(const uint8_t *obmc, const int obmc_stride, uint8_
 int ff_snow_get_buffer(SnowContext *s, AVFrame *frame)
 {
     int ret, i;
+    int edges_needed = av_codec_is_encoder(s->avctx->codec);
 
-    frame->width  = s->avctx->width  + 2 * EDGE_WIDTH;
-    frame->height = s->avctx->height + 2 * EDGE_WIDTH;
+    frame->width  = s->avctx->width ;
+    frame->height = s->avctx->height;
+    if (edges_needed) {
+        frame->width  += 2 * EDGE_WIDTH;
+        frame->height += 2 * EDGE_WIDTH;
+    }
     if ((ret = ff_get_buffer(s->avctx, frame, AV_GET_BUFFER_FLAG_REF)) < 0)
         return ret;
+    if (edges_needed) {
         for (i = 0; frame->data[i]; i++) {
             int offset = (EDGE_WIDTH >> (i ? s->chroma_v_shift : 0)) *
                             frame->linesize[i] +
@@ -82,6 +88,7 @@ int ff_snow_get_buffer(SnowContext *s, AVFrame *frame)
         }
         frame->width  = s->avctx->width;
         frame->height = s->avctx->height;
+    }
 
     return 0;
 }