Proposed are a control device and a method for controlling the transmission of a video data stream over a network to a network user device. The present invention involves storing video data segments in a data storage entity, receiving a query from at least one network user device, determining the current parameters of the at least one network user device, changing, on the basis of the determined parameters of the network user device, the video data segments stored in the data storage entity, and transmitting the changed video data segments to the network user device in response to the query. The present invention is characterized in that the video data segments stored in the data storage entity are changed by means of changing the bit rate of the video data segments by means of transcoding each video data segment in real-time. The present technical solution makes it possible to control the transmission of a video data stream over a network to a user device, and is directed at enhancing speed, simplicity and cost-effectiveness, with minimal losses of quality and maximum user satisfaction.