HLS

HLS chops a stream into short media files, typically 1 to 4 seconds each, and serves them over ordinary HTTPS with a playlist telling the player what to fetch next. Almost every stream reaches a viewer this way. It is also why quality steps up and down mid-watch. On the ingest side YouTube lists HLS as the advanced option next to the default RTMPS, and an encoder sending it can use HEVC and HDR, which RTMP cannot carry, so it suits 4K work. The trade is latency, because a segment has to be finished before it can be sent, which pushes live chat further behind the action.