VideoOverlayComposition.blend
bool blend(gstvideo.video_frame.VideoFrame videoBuf)Blends the overlay rectangles in comp on top of the raw video data contained in video_buf. The data in video_buf must be writable and mapped appropriately.
Since video_buf data is read and will be modified, it ought be mapped with flag GST_MAP_READWRITE.
Parameters
videoBuf | a #GstVideoFrame containing raw video data in a supported format. It should be mapped using GST_MAP_READWRITE |