A method for equalizing the size of the data packets by blocks of a multimedia stream including a succession of data packets of variable sizes to be transmitted in real time from a transmitter to one or more receivers, characterised in that it includes the following steps: In the transmitter, - storing a group of N data packets in a buffer memory, where N is a predefined integer, - computing the average size Tm of a packet from the different sizes of the said N packets, - generating a base stream including N data packets to be transmitted, where each has a size equal either to the rounded-down integer part └Tm┘, or to the rounded-up integer part └Tm┘ of the said average size, and at least one additional stream including N redundant data packets computed from the base stream packets, having the same size as the said base stream packets, and intended to enable the receiver to restore any lost packets if the loss rate is greater than a predefined threshold, - assessing the reception conditions of the transmitted streams, - transmitting to the receivers, either only the base stream if there is no loss of packets, or the base stream and at least one additional stream if packet loss occurs and if the loss rate is greater than a predefined threshold, wherein said multimedia stream is transmitted in a multicast system, with at least two layers using at least two multicast groups, where a first multicast group is used for the transmission of the base stream and at least one other multicast group is used for the transmission of at least one FEC stream, and configuring the receivers for receiving either only the base stream if there is no loss of packets, or the base stream and at least one additional stream if packet loss occurs and if the loss rate is greater than a predefined threshold. In the transmitter, - storing a group of N data packets in a buffer memory, where N is a predefined integer, - computing the average size Tm of a packet from the different sizes of the said N packets, - generating a base stream including N data packets to be transmitted, where each has a size equal either to the rounded-down integer part └Tm┘, or to the rounded-up integer part └Tm┘ of the said average size, and at least one additional stream including N redundant data packets computed from the base stream packets, having the same size as the said base stream packets, and intended to enable the receiver to restore any lost packets if the loss rate is greater than a predefined threshold, - assessing the reception conditions of the transmitted streams, - transmitting to the receivers, either only the base stream if there is no loss of packets, or the base stream and at least one additional stream if packet loss occurs and if the loss rate is greater than a predefined threshold, wherein said multimedia stream is transmitted in a multicast system, with at least two layers using at least two multicast groups, where a first multicast group is used for the transmission of the base stream and at least one other multicast group is used for the transmission of at least one FEC stream, and configuring the receivers for receiving either only the base stream if there is no loss of packets, or the base stream and at least one additional stream if packet loss occurs and if the loss rate is greater than a predefined threshold. - storing a group of N data packets in a buffer memory, where N is a predefined integer, - computing the average size Tm of a packet from the different sizes of the said N packets, - generating a base stream including N data packets to be transmitted, where each has a size equal either to the rounded-down integer part └Tm┘, or to the rounded-up integer part └Tm┘ of the said average size, and at least one additional stream including N redundant data packets computed from the base stream packets, having the same size as the said base stream packets, and intended to enable the receiver to restore any lost packets if the loss rate is greater than a predefined threshold, - assessing the reception conditions of the transmitted streams, - transmitting to the receivers, either only the base stream if there is no loss of packets, or the base stream and at least one additional stream if packet loss occurs and if the loss rate is greater than a predefined threshold, wherein said multimedia stream is transmitted in a multicast system, with at least two layers using at least two multicast groups, where a first multicast group is used for the transmission of the base stream and at least one other multicast group is used for the transmission of at least one FEC stream, and configuring the receivers for receiving either only the base stream if there is no loss of packets, or the base stream and at least one additional stream if packet loss occurs and if the loss rate is greater than a predefined threshold.