Data stream encoding where encoding technique selected according to available power

An indication of an amount of available power is received 512, 513, 514 from a power management module 510 (180, fig. 1). A digital data stream is encoded by an encoder (140, fig. 1) using a first encoding technique if the amount is above a given threshold or else using a second encoding technique if the amount is equal to or below the threshold. The first encoding technique may require more power than the second encoding technique. The selected technique may represent video image quality, for example, where higher quality video 520, 530 requires more power than lower quality video 540, 550. The available power may be indicated for a sequence of amounts at corresponding time instances, the encoding technique being dynamically selected according to the amount of power available at a given instance of time. The encoding techniques may be implemented by corresponding logic blocks in the encoder, those blocks not required at any time being switched off.