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>

Merges Libav commit 04f3bd349651.

3 files changed, 21 insertions, 1 deletions

diff --git a/libavutil/frame.c b/libavutil/frame.c
index a08e0c5..2913982 100644
--- a/libavutil/frame.c
+++ b/libavutil/frame.c
@@ -379,6 +379,13 @@ FF_DISABLE_DEPRECATION_WARNINGS
 FF_ENABLE_DEPRECATION_WARNINGS
 #endif
 
+    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;
 }
 
@@ -513,6 +520,8 @@ void av_frame_unref(AVFrame *frame)
 
     av_buffer_unref(&frame->hw_frames_ctx);
 
+    av_buffer_unref(&frame->opaque_ref);
+
     get_frame_defaults(frame);
 }
 
diff --git a/libavutil/frame.h b/libavutil/frame.h
index b450092..2b1dc2f 100644
--- a/libavutil/frame.h
+++ b/libavutil/frame.h
@@ -538,6 +538,17 @@ typedef struct AVFrame {
      * AVHWFramesContext describing the frame.
      */
     AVBufferRef *hw_frames_ctx;
+
+    /**
+     * AVBufferRef for free use by the API user. FFmpeg will never check the
+     * contents of the buffer ref. FFmpeg 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;
 
 /**
diff --git a/libavutil/version.h b/libavutil/version.h
index 8866064..a8b00bf 100644
--- a/libavutil/version.h
+++ b/libavutil/version.h
@@ -79,7 +79,7 @@
  */
 
 #define LIBAVUTIL_VERSION_MAJOR  55
-#define LIBAVUTIL_VERSION_MINOR  46
+#define LIBAVUTIL_VERSION_MINOR  47
 #define LIBAVUTIL_VERSION_MICRO 100
 
 #define LIBAVUTIL_VERSION_INT   AV_VERSION_INT(LIBAVUTIL_VERSION_MAJOR, \