How to get the real-time frame rate of the preview?

[ALLEN X]

As the title, is there any methods can help me get the real-time frame rate?

[Scott Nien]

One possible way is to invoke internal API mPreviewView.setFrameUpdateListener() and setImplementationMode to COMPATIBLE.   Unfortunately there is no public API exposing the same functionality unless you implement your custom view for the preview. 

see https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:camera/integration-tests/extensionstestapp/src/main/java/androidx/camera/integration/extensions/CameraExtensionsActivity.java;drc=4f39b74c22272ab84ca5f3ff1c2ad2a61e701b56;l=255 for the sample codes. 

On Tue, May 9, 2023 at 5:44 PM 'ALLEN X' via Android CameraX Discussion Group <camerax-d...@android.com> wrote:

As the title, is there any methods can help me get the real-time frame rate?

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[Eino-Ville Talvala]

I think you could also use Camera2Interop's setSessionCaptureCallback to receive the preview CaptureResult objects in onCaptureCompleted, which include a timestamp for start of exposure.

Then you can calculate the time between starts of exposure to get the current frame duration and thus the frame rate.  Note that this is a bit tricky because when exposure time changes, the time between exposure starts isn't equal to the frame duration, so ideally you'd also include the exposure time in the calculation (but that's not available on every device): 

   frame_duration = (frame[N+1].timestamp + frame[N+1].exposureTime) - (frame[N].timestamp + frame[N].exposureTime) 

   fps = 1/ frame_duration

You can also just look at the frame duration field when the device supports listing that, but the timestamp is always available.

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