Fabian Deutsch wrote the OpenCL support for GStreamer and has made it available as gst-plugins-cl. This support allows for an OpenCL kernel to be run against a video stream in the GStreamer pipeline. This support could allow for video filters to be applied while all of the work is being done by an OpenCL-supportive GPU, among other potential use-cases.
What also makes it a bit more interesting is that this OpenCL support was written in Vala.
For those wanting to learn more information read Fabian's blog post or see the Git repository.