A method for communication includes providing an item of media content for streaming in a plurality of versions having different, respective bit rates. The media content is streamed from a server to a client by transmitting a first version of the item over a network at a first bit rate from the server to the client via a server buffer associated with the server and monitoring a fill level of the server buffer while streaming the media content. The server switches to transmitting a second version of the item at a second bit rate, different from the first bit rate, to the client in response to a change in the fill level of the server buffer.