A server for data streaming encodes multimedia signals at bit rates compatible with a connection of time-varying conditions and informs a client receiving a multimedia signal of changing bit rates and causes of change. The server supports several clients and includes a flow controller and at least one encoder. The flow controller derives metrics from measurements to determine a permissible transmission rate from the server to each active client. An encoder adapts individual transmission rates of signals according to respective permissible transmission rates. An overlay module, coupled to a multimedia signal source, the flow controller, and an encoder, superimposes informative insertions indicating permissible transmission rates and associated metrics on a multimedia signal to inform a client of changing transmission rates and causes of change. An informative insertion has a predefined duration and is sent either periodically or following a substantial change of network conditions.