avcodec/encode: Always use intermediate buffer in ff_alloc_packet2()

Up until now, ff_alloc_packet2() has a min_size parameter:
It is supposed to be a lower bound on the final size of the packet
to allocate. If it is not too far from the upper bound (namely,
if it is at least half the upper bound), then ff_alloc_packet2()
already allocates the final, already refcounted packet; if it is
not, then the packet is not refcounted and its data only points to
a buffer owned by the AVCodecContext (in this case, the packet will
be made refcounted in encode_simple_internal() in libavcodec/encode.c).
The goal of this was to avoid data copies and intermediate buffers
if one has a precise lower bound.

Yet those encoders for which precise lower bounds exist have recently
been switched to ff_get_encode_buffer() (which automatically allocates
final buffers), leaving only two encoders to actually set the min_size
to something else than zero (namely aliaspixenc and hapenc). Both of
these encoders use a very low lower bound that is not helpful in any
nontrivial case.

This commit therefore removes the min_size parameter as well as the
codepath in ff_alloc_packet2() for the allocation of final buffers.
Furthermore, the function has been renamed to ff_alloc_packet() and
moved to encode.h alongside ff_get_encode_buffer().

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

1 files changed, 15 insertions, 0 deletions

diff --git a/libavcodec/encode.h b/libavcodec/encode.h
index 9af2f42483..c9cec0cc80 100644
--- a/libavcodec/encode.h
+++ b/libavcodec/encode.h
@@ -44,6 +44,21 @@ int ff_encode_get_frame(AVCodecContext *avctx, AVFrame *frame);
  */
 int ff_get_encode_buffer(AVCodecContext *avctx, AVPacket *avpkt, int64_t size, int flags);
 
+/**
+ * Check AVPacket size and allocate data.
+ *
+ * Encoders supporting AVCodec.encode2() can use this as a convenience to
+ * obtain a big enough buffer for the encoded bitstream.
+ *
+ * @param avctx   the AVCodecContext of the encoder
+ * @param avpkt   The AVPacket: on success, avpkt->data will point to a buffer
+ *                of size at least `size`; the packet will not be refcounted.
+ *                This packet must be initially blank.
+ * @param size    an upper bound of the size of the packet to encode
+ * @return        non negative on success, negative error code on failure
+ */
+int ff_alloc_packet(AVCodecContext *avctx, AVPacket *avpkt, int64_t size);
+
 /*
  * Perform encoder initialization and validation.
  * Called when opening the encoder, before the AVCodec.init() call.