A portable device (200, 210) comprises a power source (70) and a processing system (15, 20, 25, 30, 35) for processing media content received from a service provider (100) via a delivery channel. A control apparatus (50, 60) determines remaining capacity of the power source (70) and receives information from the service provider (100) about available delivery parameters for an item of content. The control apparatus determines an operating duration for the device based on the delivery parameters and the remaining capacity of the power source and sends a request to the service provider (100) specifying at least one delivery parameter for delivery of the content. By specifying what format the service provider (100) should deliver the content, power savings can be made in the processing (20, 30) and rendering (25, 35) stages and in the receive chain of the portable device. Selection of delivery parameters can be automatic or under user control.