At the beginning of February AMD open-sourced its "VCE" engine code that allows for H.264 encoding on the GPU (for recent Sea Islands GPUs and other recent GPUs with a VCE 2.0 engine over VCE 1.0 that is currently unimplemented) and complements AMD's open-source Unified Video Decoder (UVD) support from last year that was a monumental and long-awaited win for open-source AMD Linux users.
The hardware encoding support is built atop the OpenMAX state tracker that was originally developed last year by AMD's staff and now lives within mainline Mesa. OpenMAX supports both hardware encoding and decoding and the OMX API can be used by multimedia frameworks like GStreamer for having wide application support. AMD's UVD support is exposed primarily along the VDPAU state tracker for its wide support too.
After Christian König published new open-source video encode patches earlier this week, they have now been pushed into mainline Mesa. Hitting Mesa this morning was the OpenMAX H.264 encoder, Radeon VCE support changes, and the initial VCE support. This makes Radeon video encoding support an exciting feature of Mesa 10.2. There's also kernel-side changes and a new firmware blob that have yet to be queued up for the Linux kernel but should appear with the Linux 3.15 kernel.