The present invention provides a live video transmission method and system and an apparatus. According to the method, an M2U device receives a UDP request sent by a client, where the UDP request includes a live channel identifier and is used to request video data of a live channel corresponding to the live channel identifier, and the live channel identifier includes a multicast address or a URL. Then, the M2U device obtains the video data corresponding to the live channel identifier, and obtains a source IP address and a source port of the UDP request, where the source IP address and the source port of the UDP request are used as a destination IP address and a destination port of a UDP unicast packet to be subsequently sent to the client.