I think it's good to leave that up to the app developer. They can choose to use the space around the notch or crop it.
"Don't mask or call special attention to key display features. Don't attempt to hide the device's rounded corners, sensor housing, or indicator for accessing the Home screen by placing black bars at the top and bottom of the screen. Don't use visual adornments like brackets, bezels, shapes, or instructional text to call special attention to these areas either."
https://developer.apple.com/ios/human-interface-guidelines/o...
> Be mindful of aspect ratio differences when reusing existing artwork. iPhone X has a different aspect ratio than 4.7" iPhones. As a result, full-screen 4.7" iPhone artwork appears cropped or letterboxed when displayed full-screen on iPhone X. Likewise, full-screen iPhone X artwork appears cropped or pillarboxed when displayed full-screen on a 4.7" iPhone. Make sure that important visual content remains in view on both display sizes.
Emphasis mine.
EDIT: Also here [1]:
> Adhere to the safe area and layout margins defined by UIKit. These layout guides ensure appropriate insetting based on the device and context. The safe area also prevents content from underlapping the status bar, navigation bar, toolbar, and tab bar. Standard system-provided views automatically adopt a safe area layout guide.
The diagram shown suggests a "safe area" even inset a little from the notch.
[1] https://developer.apple.com/ios/human-interface-guidelines/v...
> Inset essential content to prevent clipping. In general, content should be centered and symmetrically inset so it looks great in any orientation and isn't clipped by corners or the device's sensor housing, or obscured by the indicator for accessing the Home screen
...and...
> If your app currently hides the status bar, reconsider that decision on iPhone X. The display height on iPhone provides more vertical space for content than the displays of 4.7" iPhones, and the status bar occupies an area of the screen your app probably won't fully utilize.
[emphases mine]
My take is they don't want you putting a black background up there to mask it (unless all of your background is black, presumably) but you don't have to lay out around it either. For videos and photos in particular, since black is the normal background for outside the image I doubt there'll be an issue using it at the ends.
I wonder if the graphics and UI SDKs will have built-in functions to determine where these boundaries are (as they're likely to change in future models), or if developers will just be expected to work around them as best they can.