A media data live broadcast method, a device, and a system. An over the top (OTT) live proxy server device includes a processor and non-transitory computer-readable storage medium storing instructions for allocating a multicast resource to a specified channel according to a media description and resource allocation indication of the channel instructing the OTT live proxy server to allocate the multicast resource to the specified channel, the media description including at least one resolution of the specified channel and a uniform resource locator corresponding to resolution media data, and the multicast resource including a multicast group corresponding to the specified channel, obtaining, from an OTT server to which the specified channel belongs according to the media description of the specified channel, the resolution media data, converting the media data into multicast media data, and sending the multicast media data to the multicast group in a multicast manner.