The overlay plug-in is used to draw shapes like bounding boxes, lines, arrows, circles, and polygons on a given frame or image. You can display a clock on any part of the frame by using the display-clock property. This plug-in employs the VVAS overlay library to produce different shapes, text, and clocks.
The overlay metadata structure, GstVvasOverlayMeta, must be used to provide the information about the objects like, bounding boxes, lines, and arrows to be drawn. This metadata must be attached to the input buffer. For more details about this overlay metadata structure, refer to the VVAS Overlay Metadata section.
To convert metadata generated from an upstream plug-in, such as vvas_xinfer, or segmentation into GstVvasOverlayMeta, an intermediate plug-in called vvas_xmetaconvert is provided, and this can be used before the vvas_xoverlay plug-in in gstreamer pipeline.
For insight into the implementation details, refer to the vvas_xoverlay source code located at <vvas>/vvas-gst-plugins/sys/overlay/.