AVFrame: add an opaque_ref field

This is an extended version of the AVFrame.opaque field, which can be
used to attach arbitrary user information to an AVFrame.

The usefulness of the opaque field is rather limited, because it can
store only up to 32 bits of information (or 64 bit on 64 bit systems).
It's not possible to set this field to a memory allocation, because
there is no way to deallocate it correctly.

The opaque_ref field circumvents this by letting the user set an
AVBuffer, which makes the user data refcounted.
Signed-off-by: Anton Khirnov <anton@khirnov.net>

doc/APIchanges

@@ -13,6 +13,9 @@ libavutil:     2015-08-28
 
 API changes, most recent first:
 
+2017-02-11 - xxxxxxx - lavu 55.32.0 - frame.h
+  Add AVFrame.opaque_ref.
+
 2017-02-xx - xxxxxxx - lavu 55.31.1 - frame.h
   Allow passing the value of 0 (meaning "automatic") as the required alignment
   to av_frame_get_buffer().

libavutil/frame.c

@@ -317,6 +317,8 @@ void av_frame_unref(AVFrame *frame)
 
     av_buffer_unref(&frame->hw_frames_ctx);
 
+    av_buffer_unref(&frame->opaque_ref);
+
     get_frame_defaults(frame);
 }
 
@@ -440,6 +442,13 @@ FF_ENABLE_DEPRECATION_WARNINGS
         av_dict_copy(&sd_dst->metadata, sd_src->metadata, 0);
     }
 
+    av_buffer_unref(&dst->opaque_ref);
+    if (src->opaque_ref) {
+        dst->opaque_ref = av_buffer_ref(src->opaque_ref);
+        if (!dst->opaque_ref)
+            return AVERROR(ENOMEM);
+    }
+
     return 0;
 }
 

libavutil/frame.h

@@ -395,6 +395,17 @@ typedef struct AVFrame {
     /**
      * @}
      */
+
+    /**
+     * AVBufferRef for free use by the API user. Libav will never check the
+     * contents of the buffer ref. Libav calls av_buffer_unref() on it when
+     * the frame is unreferenced. av_frame_copy_props() calls create a new
+     * reference with av_buffer_ref() for the target frame's opaque_ref field.
+     *
+     * This is unrelated to the opaque field, although it serves a similar
+     * purpose.
+     */
+    AVBufferRef *opaque_ref;
 } AVFrame;
 
 /**

libavutil/version.h

@@ -54,8 +54,8 @@
  */
 
 #define LIBAVUTIL_VERSION_MAJOR 55
-#define LIBAVUTIL_VERSION_MINOR 31
-#define LIBAVUTIL_VERSION_MICRO  1
+#define LIBAVUTIL_VERSION_MINOR 32
+#define LIBAVUTIL_VERSION_MICRO  0
 
 #define LIBAVUTIL_VERSION_INT   AV_VERSION_INT(LIBAVUTIL_VERSION_MAJOR, \
                                                LIBAVUTIL_VERSION_MINOR, \