Widevine is just a way of deriving a CENC key. Widevine (and other DRM vendors) require implementors to conform to various policies. The policies they must co

Widevine is just a way of deriving a CENC key. Widevine (and other DRM vendors) require implementors to conform to various policies. The policies they must conform to prevent what you want to do and are largely enforced in hardware at this point. The app blanking the screen is just a legacy feature. Even if it didn't blank the screen, the display buffer holding the video will not be available for capture.