An adaptive control system for a media encoder configured to encode a media data stream in accordance with a set of one or more encode parameters, the system comprising: an input queue for receiving a sequence of data portions representing a media stream; and an adaptation controller configured to form an accumulation parameter indicative of an incidence of accumulation events at the input queue, each accumulation event representing the reception of an incoming data portion into the input queue while a previous data portion in the sequence is in the input queue; the adaptation controller being configured to control the encode parameters of the media encoder in dependence on the accumulation parameter.