How to optimize LL-HLS for low latency streaming
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LL-HLS builds on the successful HLS method for streaming video to - originally - Apple devices. Whereas HLS, much like its DASH counterpart, adopts segments (typically a few to 10 seconds) as the basic unit to fetch video content, LL-HLS allows fractions of a segment to be individually addressed and fetched.
This has direct implications on the latency and zapping times. The latency is not defined by the segment size, but by the part sizes since the video parts can be fetched once a part is available and not segment per segment. This makes LL-HLS suited for low latency applications where end-to-end latencies of a few seconds are required and playback closely follows the live event. The smaller parts also allow it to start more rapidly while keeping the latency small because the player can start playback before the live segment is completely available. Moreover, as we will explain in this guide, in the right conditions, video can start playback with a part and not only at segment boundaries.