HLS (HTTP Live Streaming)

HLS (HTTP Live Streaming) is a streaming protocol created by Apple that breaks audio and video into small segments, typically a few seconds long, and describes them in text playlist files with the .m3u8 extension. Players fetch the playlist and then download segments over plain HTTP.

Why it matters

Because HLS uses standard web requests, it works with ordinary web servers and CDNs, passes through firewalls and scales to large audiences. It supports adaptive bitrate streaming through a master playlist that lists multiple quality levels. The trade-off is latency: segment-based delivery adds delay compared with real-time protocols, though low-latency HLS variants reduce it.

Example

A master playlist, simplified:

#EXTM3U
#EXT-X-STREAM-INF:BANDWIDTH=3000000,RESOLUTION=1280x720
720p/index.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=1200000,RESOLUTION=854x480
480p/index.m3u8

The player picks a variant playlist, which in turn lists segment files such as seg001.ts or seg001.m4s.

Common mistakes

• Setting very short segments, which raises request overhead, or very long ones, which slows quality switching.
• Forgetting CORS headers when the player and media are on different domains; see CORS.
• Expecting a live HLS stream to have sub-second delay.

Related

• Adaptive bitrate streaming
• CDN
• Codec
• Buffering

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