Appsrc allows the application to feed buffers to a pipeline. Applications can use the
appsrc element to insert data into a GStreamer pipeline.
Unlike most GStreamer elements, Appsrc provides external API functions.
Appsink allows the application to get access to the raw buffer from the GStreamer pipeline. Appsink is a sink plugin that supports various methods for helping the application get a handle on the GStreamer data in a pipeline. Unlike most GStreamer elements, Appsink provides external API functions.
For an example, see this application.