A method of intelligently degrading the quality of content, such as video clips and music, stored on a mobile device over time. The method takes into account the probability of a user watching each item of content and either encodes the content at a lower bit-rate, or under certain circumstances, restores the content to its original quality by side-loading the content from a network content store. The bit-rate at which the content is to be encoded is linked to the probability of a piece of content being watched. If the probability of an item of content being watched is high, then the item is stored at a high bit-rate, and conversely, for low probabilities of watching, a low bit-rate is used. If required, in order to restore an item to a higher bit rate, the original high bit rate item can be requested from a network content store. The aim being to store as much content as possible in a given finite memory, but to ensure that content which is likely to be watched is not degraded.