1. A method performed by a computing system comprising one or more processors and memory, the method comprising: compressing an original content item to a baseline lossless compressed data format; binarizing the baseline lossless compressed data format to a binarized format; arithmetically coding the binarized format based on probability estimates from a recurrent neural network probability estimator; and wherein the recurrent neural network probability estimator generates probability estimates for current symbols of the binarized format to be arithmetically coded based on symbols of the binarized format that have already been arithmetically coded during the arithmetically coding the binarized format.