avcodec/packet: deprecate av_init_packet()

Once removed, sizeof(AVPacket) will stop being a part of the public ABI.
Signed-off-by: James Almer <jamrial@gmail.com>

doc/APIchanges

@@ -15,6 +15,11 @@ libavutil:     2017-10-21
 
 API changes, most recent first:
 
+2021-03-xx - xxxxxxxxxx - lavc 58.133.100 - codec.h
+  Deprecated av_init_packet(). Once removed, sizeof(AVPacket) will
+  no longer be a part of the public ABI.
+  Deprecated AVPacketList.
+
 2021-03-xx - xxxxxxxxxx - lavc 58.132.100 - codec.h
   Add AV_CODEC_CAP_OTHER_THREADS as a new name for
   AV_CODEC_CAP_AUTO_THREADS. AV_CODEC_CAP_AUTO_THREADS

libavcodec/avpacket.c

@@ -32,6 +32,7 @@
 #include "packet.h"
 #include "packet_internal.h"
 
+#if FF_API_INIT_PACKET
 void av_init_packet(AVPacket *pkt)
 {
     pkt->pts                  = AV_NOPTS_VALUE;
@@ -49,6 +50,16 @@ FF_ENABLE_DEPRECATION_WARNINGS
     pkt->side_data            = NULL;
     pkt->side_data_elems      = 0;
 }
+#endif
+
+static void get_packet_defaults(AVPacket *pkt)
+{
+    memset(pkt, 0, sizeof(*pkt));
+
+    pkt->pts             = AV_NOPTS_VALUE;
+    pkt->dts             = AV_NOPTS_VALUE;
+    pkt->pos             = -1;
+}
 
 AVPacket *av_packet_alloc(void)
 {
@@ -56,7 +67,7 @@ AVPacket *av_packet_alloc(void)
     if (!pkt)
         return pkt;
 
-    av_init_packet(pkt);
+    get_packet_defaults(pkt);
 
     return pkt;
 }
@@ -92,7 +103,7 @@ int av_new_packet(AVPacket *pkt, int size)
     if (ret < 0)
         return ret;
 
-    av_init_packet(pkt);
+    get_packet_defaults(pkt);
     pkt->buf      = buf;
     pkt->data     = buf->data;
     pkt->size     = size;
@@ -611,9 +622,7 @@ void av_packet_unref(AVPacket *pkt)
 {
     av_packet_free_side_data(pkt);
     av_buffer_unref(&pkt->buf);
-    av_init_packet(pkt);
-    pkt->data = NULL;
-    pkt->size = 0;
+    get_packet_defaults(pkt);
 }
 
 int av_packet_ref(AVPacket *dst, const AVPacket *src)
@@ -668,9 +677,7 @@ AVPacket *av_packet_clone(const AVPacket *src)
 void av_packet_move_ref(AVPacket *dst, AVPacket *src)
 {
     *dst = *src;
-    av_init_packet(src);
-    src->data = NULL;
-    src->size = 0;
+    get_packet_defaults(src);
 }
 
 int av_packet_make_refcounted(AVPacket *pkt)

libavcodec/packet.h

@@ -323,10 +323,6 @@ typedef struct AVPacketSideData {
  * packets, with no compressed data, containing only side data
  * (e.g. to update some stream parameters at the end of encoding).
  *
- * AVPacket is one of the few structs in FFmpeg, whose size is a part of public
- * ABI. Thus it may be allocated on stack and no new fields can be added to it
- * without libavcodec and libavformat major bump.
- *
  * The semantics of data ownership depends on the buf field.
  * If it is set, the packet data is dynamically allocated and is
  * valid indefinitely until a call to av_packet_unref() reduces the
@@ -338,6 +334,12 @@ typedef struct AVPacketSideData {
  * The side data is always allocated with av_malloc(), copied by
  * av_packet_ref() and freed by av_packet_unref().
  *
+ * sizeof(AVPacket) being a part of the public ABI is deprecated. once
+ * av_init_packet() is removed, new packets will only be able to be allocated
+ * with av_packet_alloc(), and new fields may be added to the end of the struct
+ * with a minor bump.
+ *
+ * @see av_packet_alloc
  * @see av_packet_ref
  * @see av_packet_unref
  */
@@ -397,10 +399,13 @@ typedef struct AVPacket {
 #endif
 } AVPacket;
 
+#if FF_API_INIT_PACKET
+attribute_deprecated
 typedef struct AVPacketList {
     AVPacket pkt;
     struct AVPacketList *next;
 } AVPacketList;
+#endif
 
 #define AV_PKT_FLAG_KEY     0x0001 ///< The packet contains a keyframe
 #define AV_PKT_FLAG_CORRUPT 0x0002 ///< The packet content is corrupted
@@ -464,6 +469,7 @@ AVPacket *av_packet_clone(const AVPacket *src);
  */
 void av_packet_free(AVPacket **pkt);
 
+#if FF_API_INIT_PACKET
 /**
  * Initialize optional fields of a packet with default values.
  *
@@ -471,8 +477,16 @@ void av_packet_free(AVPacket **pkt);
  * initialized separately.
  *
  * @param pkt packet
+ *
+ * @see av_packet_alloc
+ * @see av_packet_unref
+ *
+ * @deprecated This function is deprecated. Once it's removed,
+               sizeof(AVPacket) will not be a part of the ABI anymore.
  */
+attribute_deprecated
 void av_init_packet(AVPacket *pkt);
+#endif
 
 /**
  * Allocate the payload of a packet and initialize its fields with

libavcodec/version.h

@@ -28,7 +28,7 @@
 #include "libavutil/version.h"
 
 #define LIBAVCODEC_VERSION_MAJOR  58
-#define LIBAVCODEC_VERSION_MINOR 132
+#define LIBAVCODEC_VERSION_MINOR 133
 #define LIBAVCODEC_VERSION_MICRO 100
 
 #define LIBAVCODEC_VERSION_INT  AV_VERSION_INT(LIBAVCODEC_VERSION_MAJOR, \
@@ -165,5 +165,8 @@
 #ifndef FF_API_AUTO_THREADS
 #define FF_API_AUTO_THREADS        (LIBAVCODEC_VERSION_MAJOR < 60)
 #endif
+#ifndef FF_API_INIT_PACKET
+#define FF_API_INIT_PACKET         (LIBAVCODEC_VERSION_MAJOR < 60)
+#endif
 
 #endif /* AVCODEC_VERSION_H */

libavformat/avformat.h

@@ -954,7 +954,11 @@ typedef struct AVStream {
      * decoding: set by libavformat, must not be modified by the caller.
      * encoding: unused
      */
+#if FF_API_INIT_PACKET
     AVPacket attached_pic;
+#else
+    AVPacket *attached_pic;
+#endif
 
     /**
      * An array of side data that applies to the whole stream (i.e. the