A method for providing programs of a multicast group in an IPTV environment, comprising the steps of: a) transmitting at least one multimedia data stream representing a program via an IP-based distribution network to at least one multicast replication point to which a plurality of receiving devices (901 to 904) can be connected via a subscriber line network, the multimedia data stream containing I-frames "IF" at predetermined locations; b) generating, in said multicast replication point, a number of N mutually time-offset subgroup data streams from each arriving multimedia data stream, wherein N is greater than 1; c) determining, in response to a program request command from a receiving device (901 to 904), the subgroup data stream associated with the requested program, in which an I-frame can be transmitted to the receiving device (901 to 904) at the earliest possible time; d) transmitting the determined subgroup data stream to the receiving device (901 to 904) that requested the program; e) assigning a unique multicast address to each program selectable at a receiving device (901 to 904) and an individual address to each subgroup data stream associated with a multimedia data stream; f) converting the individual address of the subgroup data stream determined in step c) into the multicast address assigned to the selected program, so that the subgroup data stream associated with the selected program can be received by the receiving device (901 to 904); g) predefining a maximum switching time which i) defines the time offset between two subgroup data streams, and ii) defines the time at which an I-frame can be transmitted, the maximum switching time being guaranteed by performing the following steps: h) determining the time interval between two successive I-frames in the multimedia data stream; i) calculating the number N of subgroup data streams to be generated from the quotient of the determined time interval between two successive I-frames and the maximum switching time; wherein step c) comprises the steps of: c.2) monitoring the multimedia data stream arriving at the multicast replication point to identify the I-frames contained therein; c.3) restarting a counter for each identified I-frame, the counter interval corresponding to the predefined maximum switching time; and wherein step d) comprises the step of: d.2) determining the subgroup data stream to be transmitted in dependence of the current counter reading. a) transmitting at least one multimedia data stream representing a program via an IP-based distribution network to at least one multicast replication point to which a plurality of receiving devices (901 to 904) can be connected via a subscriber line network, the multimedia data stream containing I-frames "IF" at predetermined locations; b) generating, in said multicast replication point, a number of N mutually time-offset subgroup data streams from each arriving multimedia data stream, wherein N is greater than 1; c) determining, in response to a program request command from a receiving device (901 to 904), the subgroup data stream associated with the requested program, in which an I-frame can be transmitted to the receiving device (901 to 904) at the earliest possible time; d) transmitting the determined subgroup data stream to the receiving device (901 to 904) that requested the program; e) assigning a unique multicast address to each program selectable at a receiving device (901 to 904) and an individual address to each subgroup data stream associated with a multimedia data stream; f) converting the individual address of the subgroup data stream determined in step c) into the multicast address assigned to the selected program, so that the subgroup data stream associated with the selected program can be received by the receiving device (901 to 904); g) predefining a maximum switching time which i) defines the time offset between two subgroup data streams, and ii) defines the time at which an I-frame can be transmitted, the maximum switching time being guaranteed by performing the following steps: h) determining the time interval between two successive I-frames in the multimedia data stream; i) calculating the number N of subgroup data streams to be generated from the quotient of the determined time interval between two successive I-frames and the maximum switching time; c.2) monitoring the multimedia data stream arriving at the multicast replication point to identify the I-frames contained therein; c.3) restarting a counter for each identified I-frame, the counter interval corresponding to the predefined maximum switching time; and d.2) determining the subgroup data stream to be transmitted in dependence of the current counter reading.