lavu/buffer: add release function

new function allows to unref buffer and obtain its data.

Signed-off-by: Lukasz Marek <lukasz.m.luki@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavutil/buffer.c

@@ -117,6 +117,35 @@ void av_buffer_unref(AVBufferRef **buf)
     }
 }
 
+int av_buffer_release(AVBufferRef **buf, uint8_t **data)
+{
+    AVBuffer *b;
+    int ret = 0;
+
+    if (data)
+        *data = NULL;
+    if (!buf || !*buf)
+        return 0;
+    b = (*buf)->buffer;
+    av_freep(buf);
+
+    if (data && avpriv_atomic_int_get(&b->refcount) > 1) {
+        *data = av_memdup(b->data, b->size);
+        if (!*data)
+            ret = AVERROR(ENOMEM);
+    }
+
+    if (!avpriv_atomic_int_add_and_fetch(&b->refcount, -1)) {
+        if (data && !*data) {
+            ret = 0;
+            *data = b->data;
+        } else
+            b->free(b->opaque, b->data);
+        av_freep(&b);
+    }
+    return ret;
+}
+
 int av_buffer_is_writable(const AVBufferRef *buf)
 {
     if (buf->buffer->flags & AV_BUFFER_FLAG_READONLY)