Film grain is abundant in TV and movie content. It is often part of the creative intent and needs to be preserved while encoding. However, the random nature of film grain is difficult to compress using traditional coding tools. This paper describes a film grain modeling and synthesis algorithm proposed for the AV1 video codec. At the encoder, an autoregressive model of film grain is transmitted relative to a denoised signal, and the film grain strength is modeled as a function of intensity. The corresponding renoising at the decoder is implemented using an efficient block-based approach suitable for use in consumer electronic devices. Preliminary results indicate that the approach can give significant bitrate savings (up to 50%) on sequences with heavy film grain.