How to get images or videos from the headset camera

#1

In OpenXR Spec, I know OpenXR App can set the environment blend mode of “XR_ENVIRONMENT_BLEND_MODE_ADDITIVE” to make the display show the real world view.
If I do not have wrong understanding, it means the XR runtime will let the real world images that captured from the camera move to SwapChain and wait for rendering operations.
However, sometime a few operations need to directly call APIs to get images or videos from the camera.
Is there any OpenXR API that can do this thing?