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I'm integrating the Camera2 API to my Android app and test it on Samsung Galaxy Tab S2. I need to work with real time preview frames.
Here is my code:

private val onPreviewAvailableListener = ImageReader.OnImageAvailableListener reader ->
 if (reader != null) 
 val image = reader.acquireNextImage()
 if (image != null) 
 // do something with image
 image.close()
 
 


private var mPreviewRequestBuilder: CaptureRequest.Builder? = null
private lateinit var mPreviewSize: Size

private fun configurePreview() 
 // some code here 
 // ... 

 previewImageReader = ImageReader.newInstance(
 mPreviewSize.width,
 mPreviewSize.height,
 ImageFormat.YUV_420_888,
 2
 )
 previewImageReader?.setOnImageAvailableListener(onPreviewAvailableListener, backgroundHandler)

 // some code here 
 // ... 


// other code

private fun createCameraPreviewSession() 
 mPreviewRequestBuilder = mCameraDevice?.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW)
 mPreviewRequestBuilder?.addTarget(previewImageReader?.surface)
 mPreviewRequestBuilder?.addTarget(surface) // surfaceView

 mCameraDevice?.createCaptureSession(
 Arrays.asList(previewImageReader?.surface, surface),
 object : CameraCaptureSession.StateCallback() ,
 null /* null handler */

I need images in onPreviewAvailableListener to be of a high resolution. And they are. The resolution is not too high. Something about 1280*720. The problem is that my preview TextureView lags as if 15 FPS was set.

Maybe I can decrease the frequency of images coming to onPreviewAvailableListener. I tried setting a flag to only handle every 10-th o 20-th image in onPreviewAvailableListener's onImageAvailable, but nothing changed:

private val onPreviewAvailableListener = object: ImageReader.OnImageAvailableListener 

 private var counter = 10 

 fun onImageAvailable(reader : ImageReader) 
 if (counter % 10 == 0) 
 if (reader != null) 
 val image = reader.acquireNextImage()
 if (image != null) 
 // do something with image
 image.close()
 
 
 
 if (counter == Int.MAX_VALUE) 
 counter = 0
 else 
 counter++
 
 

I also tried creating a new background thread specially for onPreviewAvailableListener so that its callback method is called on that thread. Nothing changed either:

previewImageReader?.setOnImageAvailableListener(onPreviewAvailableListener, previewImageReaderHandler) /* it's NOT backgroundHandler */