This pair of elements, inspired from shmsink/shmsrc, send unix file descriptors (e.g. memfd, dmabuf) from one sink to multiple source elements in other processes. The unixfdsink proposes a memfd/shm allocator, which causes for example videotestsrc to write directly into memories that can be transfered to other processes without copying. Sponsored-by: Netflix Inc. Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5328>