There is only one file type that uses the .NFV extension:
Netflix Video File
An NFV file is a video file created by the Netflix streaming app, which is available for Android and iOS. It contains encrypted video for a movie or show downloaded through the app. NFV files are used for offline viewing, a feature launched in December 2016. It allows you to watch movies or shows when not connected to the Internet.
Updated: November 8, 2018