avutil/mastering_display_metadata: add a new allocator function that returns a size

av_mastering_display_metadata_alloc() is not useful in scenarios where you need to
know the runtime size of AVMasteringDisplayMetadata.

Signed-off-by: James Almer <jamrial@gmail.com>

doc/APIchanges

@@ -2,6 +2,9 @@ The last version increases of all libraries were on 2024-03-07
 
 API changes, most recent first:
 
+2024-04-11 - xxxxxxxxxx - lavu 59.15.100 - frame.h
+  Add av_mastering_display_metadata_alloc_size().
+
 2024-04-11 - xxxxxxxxxx - lavu 59.14.100 - frame.h
   Add av_frame_side_data_add() and av_frame_side_data_remove().
   Add AV_FRAME_SIDE_DATA_FLAG_REPLACE.

libavutil/mastering_display_metadata.c

@@ -18,6 +18,7 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
+#include <stddef.h>
 #include <stdint.h>
 #include <string.h>
 
@@ -29,6 +30,18 @@ AVMasteringDisplayMetadata *av_mastering_display_metadata_alloc(void)
     return av_mallocz(sizeof(AVMasteringDisplayMetadata));
 }
 
+AVMasteringDisplayMetadata *av_mastering_display_metadata_alloc_size(size_t *size)
+{
+    AVMasteringDisplayMetadata *mastering = av_mallocz(sizeof(AVMasteringDisplayMetadata));
+    if (!mastering)
+        return NULL;
+
+    if (size)
+        *size = sizeof(*mastering);
+
+    return mastering;
+}
+
 AVMasteringDisplayMetadata *av_mastering_display_metadata_create_side_data(AVFrame *frame)
 {
     AVFrameSideData *side_data = av_frame_new_side_data(frame,

libavutil/mastering_display_metadata.h

@@ -77,6 +77,15 @@ typedef struct AVMasteringDisplayMetadata {
  */
 AVMasteringDisplayMetadata *av_mastering_display_metadata_alloc(void);
 
+/**
+ * Allocate an AVMasteringDisplayMetadata structure and set its fields to
+ * default values. The resulting struct can be freed using av_freep().
+ *
+ * @return An AVMasteringDisplayMetadata filled with default values or NULL
+ *         on failure.
+ */
+AVMasteringDisplayMetadata *av_mastering_display_metadata_alloc_size(size_t *size);
+
 /**
  * Allocate a complete AVMasteringDisplayMetadata and add it to the frame.
  *

libavutil/version.h

@@ -79,7 +79,7 @@
  */
 
 #define LIBAVUTIL_VERSION_MAJOR  59
-#define LIBAVUTIL_VERSION_MINOR  14
+#define LIBAVUTIL_VERSION_MINOR  15
 #define LIBAVUTIL_VERSION_MICRO 100
 
 #define LIBAVUTIL_VERSION_INT   AV_VERSION_INT(LIBAVUTIL_VERSION_MAJOR, \