int perms, int w, int h);
AVFilterBufferRef *ff_null_get_video_buffer(AVFilterLink *link, int perms, int w, int h);
+/**
+ * Request a picture buffer with a specific set of permissions.
+ *
+ * @param link the output link to the filter from which the buffer will
+ * be requested
+ * @param perms the required access permissions
+ * @param w the minimum width of the buffer to allocate
+ * @param h the minimum height of the buffer to allocate
+ * @return A reference to the buffer. This must be unreferenced with
+ * avfilter_unref_buffer when you are finished with it.
+ */
+AVFilterBufferRef *ff_get_video_buffer(AVFilterLink *link, int perms,
+ int w, int h);
+
+int ff_inplace_start_frame(AVFilterLink *link, AVFilterBufferRef *picref);
+int ff_null_start_frame(AVFilterLink *link, AVFilterBufferRef *picref);
+int ff_null_draw_slice(AVFilterLink *link, int y, int h, int slice_dir);
+int ff_null_end_frame(AVFilterLink *link);
+
+/**
+ * Notify the next filter of the start of a frame.
+ *
+ * @param link the output link the frame will be sent over
+ * @param picref A reference to the frame about to be sent. The data for this
+ * frame need only be valid once draw_slice() is called for that
+ * portion. The receiving filter will free this reference when
+ * it no longer needs it.
+ *
+ * @return >= 0 on success, a negative AVERROR on error. This function will
+ * unreference picref in case of error.
+ */
+int ff_start_frame(AVFilterLink *link, AVFilterBufferRef *picref);
+
+/**
+ * Pass video frame along and keep an internal reference for later use.
+ */
+int ff_null_start_frame_keep_ref(AVFilterLink *inlink, AVFilterBufferRef *picref);
-void ff_null_start_frame(AVFilterLink *link, AVFilterBufferRef *picref);
-void ff_null_draw_slice(AVFilterLink *link, int y, int h, int slice_dir);
-void ff_null_end_frame(AVFilterLink *link);
+/**
+ * Notify the next filter that the current frame has finished.
+ *
+ * @param link the output link the frame was sent over
+ *
+ * @return >= 0 on success, a negative AVERROR on error
+ */
+int ff_end_frame(AVFilterLink *link);
+
+/**
+ * Send a slice to the next filter.
+ *
+ * Slices have to be provided in sequential order, either in
+ * top-bottom or bottom-top order. If slices are provided in
+ * non-sequential order the behavior of the function is undefined.
+ *
+ * @param link the output link over which the frame is being sent
+ * @param y offset in pixels from the top of the image for this slice
+ * @param h height of this slice in pixels
+ * @param slice_dir the assumed direction for sending slices,
+ * from the top slice to the bottom slice if the value is 1,
+ * from the bottom slice to the top slice if the value is -1,
+ * for other values the behavior of the function is undefined.
+ *
+ * @return >= 0 on success, a negative AVERROR on error.
+ */
+int ff_draw_slice(AVFilterLink *link, int y, int h, int slice_dir);
#endif /* AVFILTER_VIDEO_H */