avcodec/utils: do not use internal->byte_buffer when little downsizing is expected

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/utils.c

@@ -1789,7 +1789,7 @@ int ff_alloc_packet2(AVCodecContext *avctx, AVPacket *avpkt, int64_t size, int64
         return AVERROR(EINVAL);
     }
 
-    if (avctx) {
+    if (avctx && 2*min_size < size) { // FIXME The factor needs to be finetuned
         av_assert0(!avpkt->data || avpkt->data != avctx->internal->byte_buffer);
         if (!avpkt->data || avpkt->size < size) {
             av_fast_padded_malloc(&avctx->internal->byte_buffer, &avctx->internal->byte_buffer_size, size);