A method for interfacing a plurality of videoconferencing client devices the method comprising, in a computer server (5) connected to a client devices:—receiving a first client video stream (7) from the video routing client (4);—tagging a video image of the first client video stream received from the video routing client;—sending, through a bidirectional communication channel (14), the first client video stream (21) to a mixing client (2);—receiving, through the bidirectional communication channel with the mixing client, a mixed video stream (15) from said mixing client;—detecting in the mixed video stream received from the mixing client a video image portion which is different from the tagged video image of the first client video stream;—extracting the detected video image portion from the mixed video stream;—generating a second client video stream (23) from the extracted video image portion;—sending the second client video stream to the video routing client.