This report describes a low-bandwidth videoconferencing applications on the Internet using the IP multicast extensions and the User Datagram Protocol (UDP) transport protocol. The video coder-decoder is a software implementation of the CCITT recommendation H.261 originally developped for the Integrated Services Digital Network (ISDN). Until now, H.261 codecs have been implemented in hardware. We find that the mean output rate of the coder is less than 30kb/s, thus making videoconferencing applications possible over low-speed networks such as the Internet. After a brief overview of the different data copression techniques and a description of the recommendation H.261, we describe in more details IVS, our videoconferencing application which is freely available on the public domain.