avcodec/zmbvenc: Avoid copying packet data, allow user-supplied buffers

Here the packet size is known before allocating the packet because
the encoder itself works with an internal buffer, so one can use
this information to avoid the implicit use of another intermediate
buffer for the packet data; one can also switch to
ff_get_encode_buffer() and directly use user-supplied buffers.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavcodec/zmbvenc.c

@@ -30,6 +30,7 @@
 #include "libavutil/common.h"
 #include "libavutil/intreadwrite.h"
 #include "avcodec.h"
+#include "encode.h"
 #include "internal.h"
 
 #include <zlib.h>
@@ -275,7 +276,7 @@ static int encode_frame(AVCodecContext *avctx, AVPacket *pkt,
     }
 
     pkt_size = c->zstream.total_out + 1 + 6*keyframe;
-    if ((ret = ff_alloc_packet2(avctx, pkt, pkt_size, 0)) < 0)
+    if ((ret = ff_get_encode_buffer(avctx, pkt, pkt_size, 0)) < 0)
         return ret;
     buf = pkt->data;
 
@@ -427,6 +428,7 @@ const AVCodec ff_zmbv_encoder = {
     .long_name      = NULL_IF_CONFIG_SMALL("Zip Motion Blocks Video"),
     .type           = AVMEDIA_TYPE_VIDEO,
     .id             = AV_CODEC_ID_ZMBV,
+    .capabilities   = AV_CODEC_CAP_DR1,
     .priv_data_size = sizeof(ZmbvEncContext),
     .init           = encode_init,
     .encode2        = encode_frame,