A method of selecting an encoding specification for encoding audio and/or video data to be streamed between a user-device and a remote device, the user-device being operable to communicate with the remote device via a digital subscriber line for a portion of a path between the user-device and the remote device, said portion extending between a user-side digital subscriber line modem device and a digital subscriber line aggregation transceiver device, the method comprising: at either or both of said user-side digital subscriber line modem device and said digital subscriber line aggregation transceiver device, measuring digital subscriber line performance data in respect of data communications at a plurality of different times on the digital subscriber line between the user-side digital subscriber line modem device and the digital subscriber line aggregation transceiver device; in dependence on the digital subscriber line performance data measured in respect of data communications at said plurality of different times on the digital subscriber line between the user-side digital subscriber line modem device and the digital subscriber line aggregation transceiver device, determining one or more data communication characteristics in respect of data communications over a monitoring period including said plurality of different times on the digital subscriber line between the user-side digital subscriber line modem device and the digital subscriber line aggregation transceiver device; and selecting an encoding specification for encoding said data to be streamed between said user-device and said remote device, the selection of said encoding specification being made in dependence on the data communication characteristics determined in respect of data communications over said monitoring period on the digital subscriber line. at either or both of said user-side digital subscriber line modem device and said digital subscriber line aggregation transceiver device, measuring digital subscriber line performance data in respect of data communications at a plurality of different times on the digital subscriber line between the user-side digital subscriber line modem device and the digital subscriber line aggregation transceiver device; in dependence on the digital subscriber line performance data measured in respect of data communications at said plurality of different times on the digital subscriber line between the user-side digital subscriber line modem device and the digital subscriber line aggregation transceiver device, determining one or more data communication characteristics in respect of data communications over a monitoring period including said plurality of different times on the digital subscriber line between the user-side digital subscriber line modem device and the digital subscriber line aggregation transceiver device; and selecting an encoding specification for encoding said data to be streamed between said user-device and said remote device, the selection of said encoding specification being made in dependence on the data communication characteristics determined in respect of data communications over said monitoring period on the digital subscriber line.