Methods and transcoding proxies for transcoding media streams are described. In one embodiment, a method for transcoding a media stream that is delivered to an end-user device over a communications network involves selecting a transcoding technique for the media stream, transcoding a portion of the media stream using the selected transcoding technique, streaming the transcoded portion of the media stream to the end-user device, while the transcoded portion of the media stream is being streamed to the end-user device, detecting a change in a condition of the communications network, selecting a different transcoding technique in response to the change in the condition of the communications network, transcoding a subsequent portion of the media stream using the different transcoding technique, and streaming the transcoded subsequent portion of the media stream to the end-user device. Other embodiments are also described.