avcodec: Add a min size parameter to ff_alloc_packet2()

This parameter can be used to inform the allocation code about how much
downsizing might occur, and can be used to optimize how to allocate the
packet

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

libavcodec/libutvideoenc.cpp

@@ -143,7 +143,7 @@ static int utvideo_encode_frame(AVCodecContext *avctx, AVPacket *pkt,
     uint8_t *dst;
 
     /* Alloc buffer */
-    if ((ret = ff_alloc_packet2(avctx, pkt, utv->buf_size)) < 0)
+    if ((ret = ff_alloc_packet2(avctx, pkt, utv->buf_size, 0)) < 0)
         return ret;
 
     dst = pkt->data;