https://www.slashcam.com/news/single/Netflix-removes-movie-noise--saves-30--bandwidth-a-17337.html
”’Filmmaker Parker Gibbons has drawn attention to a very interesting fact: Netflix removes film noise before streaming its movies and artificially adds it back when decoding. This is because digitally shot films are actually free of any film grain, the very specific (not to be confused with noise caused by too little light) noise that occurs in analog filming. But this type of noise has become so associated with “real” motion pictures through the long history of film (as a component of the film look) that it is unconsciously perceived by many viewers as an important feature of a motion picture.
…
This leads to a difficult-to-resolve contradiction between, on the one hand, film material that is as compressible and noise-free as possible, and, on the other hand, the noise caused by film grain that is desirable for the film look. Netflix has found a very special solution to resolve this contradiction. It uses a very special function of the open source 
AV1 video codec, which Netflix has been using for a long time, namely the artificial synthesis of film grain. Thus, film noise is first analyzed using statistical methods before compression and then removed for efficient compression. According to Netflix, this saves around 30% of the data during transmission.”’
