Wayland Protocols 1.2 Adds Presentation Time Support For Better Video Playback
Written by Michael Larabel in Wayland on 7 March 2016 at 06:16 AM EST. Add A Comment
WAYLAND --
Wayland-Protocols 1.2 was released this morning as the newest version of this official Wayland protocol collection.

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.
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Michael Larabel is the principal author of Phoronix.com and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 10,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated benchmarking software. He can be followed via Twitter or contacted via MichaelLarabel.com.

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