Phase Sync is a frame timing management technique used to manage latency adaptively. It is available for Quest and Quest 2 apps as an option in Unreal Engine Integration v23 and later.

To activate Phase Sync adaptive frame timing in Unreal Engine, see the Enable Phase Sync section.

More About 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.

Chart comparing Phase Sync to Fixed Latency

Note the following when Phase Sync is enabled:

No additional performance overhead: Phase Sync does not increase an app’s performance demands.

Sensitive to workload fluctuations: If the app’s workload fluctuates or spikes frequently, Phase Sync might cause more stale frames.

Complements late-latching: Phase Sync and late-latching often work well together.

Extra latency mode: If both extra latency mode and Phase Sync are enabled, the extra latency mode will be ignored.

Enable Phase Sync

You can enable Phase Sync in Unreal Engine if you have Unreal Engine Integration v23 or later, available from the Oculus-VR GitHub distribution of Unreal Engine⁠.

Note: If you are not subscribed to the private EpicGames/UnrealEngine repository and logged in to GitHub, you will receive a 404 error when you click the link. For more information, see Version Compatibility Reference.

To enable Phase Sync:

Open your project in Unreal Engine.

Click Edit > Project Settings, and then go to Plugins > OculusVR.

In the Mobile section, select the Phase Sync checkbox.

The Phase Sync option in the Project Settings dialog box

Testing Phase Sync

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

If Phase Sync is not active, the Lat value is either Lat=0 or Lat=1, indicating extra latency mode.

If Phase Sync is active, the Lat value is Lat=-1, indicating the latency is managed dynamically.

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 using an adb shell setprop. You must restart the app after changing the setprop for the change to have effect.

Turn off: adb shell setprop debug.oculus.phaseSync 0

Turn on: adb shell setprop debug.oculus.phaseSync 1