Phase Sync is a frame timing management technique used to manage latency adaptively. It is available for Meta Quest apps as an option in the latest the Meta XR Core SDK.

To activate Phase Sync adaptive frame timing, see Enable Phase Sync.

Phase Sync offers an alternative to the fixed-latency mode for managing frame timing in Meta Quest apps. In fixed-latency mode, frames are composited as early as possible to avoid missing the current frame and reusing a stale one. Stale frames can negatively affect the user experience.

Unlike fixed-latency, Phase Sync adapts frame timing based on the app’s workload. Its goal is to complete frame rendering just before the compositor needs it, reducing rendering latency without missing frames.

The following image shows the difference between a fixed latency and when Phase Sync is enabled for a typical multi-threaded VR app.

Note the following when Phase Sync is enabled:

After enabling Phase Sync in your app, you can verify that it is active and see how much latency it has saved by examining the logcat logs.

adb logcat -s VrApi

The Prd value indicates the render latency as measured by the runtime. To calculate how much latency Phase Sync has saved, compare the Prd values between when Phase Sync is active and not active. For example, if the Prd with Phase Sync is 35ms and the Prd without is 45ms, you saved 10ms of latency with Phase Sync.

To more easily compare performance with and without Phase Sync, you can turn it on and off with an adb shell setprop. You must restart the app after changing the setprop for the change to have effect.