The Wayland-Protocols 1.2 release adds "presentation time" to the protocol. Presentation-time is based off the protocol originally found in Weston 1.10 and is now considered a stable protocol with no changes since December 2014. The protocol is self-described as:
The main feature of this interface is accurate presentation timing feedback to ensure smooth video playback while maintaining audio/video synchronization. Some features use the concept of a presentation clock, which is defined in presentation.clock_id event.
Request 'feedback' can be regarded as an additional wl_surface method. It is part of the double-buffered surface state update mechanism, where other requests first set up the state and then wl_surface.commit atomically applies the state into use. In other words, wl_surface.commit submits a content update.
When the final realized presentation time is available, e.g. after a framebuffer flip completes, the requested presentation_feedback.presented events are sent. The final presentation time can differ from the compositor's predicted display update time and the update's target time, especially when the compositor misses its target vertical blanking period.
The addition of presentation-time is the main change with Wayland-Protocols 1.2, which was announced this morning on the Wayland-devel list.