avcodec: add a get_encode_buffer() callback to AVCodecContext

This callback is functionally the same as get_buffer2() is for decoders, and
implements for the new encode API the functionality of the old encode API had
where the user could provide their own buffers.

Reviewed-by: Lynne <dev@lynne.ee>
Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Reviewed-by: Mark Thompson <sw@jkqxz.net>
Signed-off-by: James Almer <jamrial@gmail.com>

libavcodec/encode.h

@@ -24,6 +24,7 @@
 #include "libavutil/frame.h"
 
 #include "avcodec.h"
+#include "packet.h"
 
 /**
  * Called by encoders to get the next frame for encoding.
@@ -36,4 +37,11 @@
  */
 int ff_encode_get_frame(AVCodecContext *avctx, AVFrame *frame);
 
+/**
+ * Get a buffer for a packet. This is a wrapper around
+ * AVCodecContext.get_encode_buffer() and should be used instead calling get_encode_buffer()
+ * directly.
+ */
+int ff_get_encode_buffer(AVCodecContext *avctx, AVPacket *avpkt, int64_t size, int flags);
+
 #endif /* AVCODEC_ENCODE_H */