GStreamer 1.12 is bringing waylandsink DMA-BUF importation support so zero-copy multimedia playback will now work under Wayland. GStreamer 1.12 is also bringing Fraunhofer FDK AAC encoder/decoder support, Intel Media SDK support for accelerated video encode/decode on embedded Linux and Windows, OpenCV improvements, CineForm support, and more.
Our friends over at Collabora have posted a blog post with more details on GStreamer 1.12 from their developer perspective if you are interested.
There is also the official release notes for 1.12. Some of the other items mention include videscale/videoconvert supporting multi-threaded scaling/conversion, x264enc can now use multiple x264 library versions compiled for different bit depths, API additions, OpenGL fixes, and more.