Simon Willison’s Weblog

Unlike progressive downloads, HTTP Live Streaming actually does stream content in real time, although there can be a latency of as much as 30 seconds. [...] the content to be broadcast is encoded into an MPEG transport stream and chopped into segments that are around ten seconds long. Rather than getting a continuous stream of new data over RTSP, the new protocol simply asks for the first couple clips, then asks for additional clips as needed. This works great through firewalls, and doesn't require any special servers because any standard web server can deliver the chopped up video segments.

— Prince McLean