An apparatus for encoding frames of a sequence of source frames of video image data to be encoded. The apparatus includes encoding circuitry configured to encode the source frames using reference frames. The apparatus also includes monitoring circuitry configured to, when the encoding circuitry is encoding a source frame using one or more reference frames, monitor the memory bandwidth being used when using the one or more reference frames when encoding the source frame. The apparatus further includes encoding circuitry that is operable to, in response to the monitored memory bandwidth being greater than a threshold, to control the encoding circuitry to encode a subsequent part of the source frame using a modified video encoding process to restrict the memory bandwidth usage when using one or more reference frames when encoding a subsequent part of a source frame.