Video segment / chunk
A video segment (or chunk) is a short piece of a video, usually 2 to 10 seconds long, that a streaming player downloads one after another. Protocols such as HLS and DASH split each rendition into these segments and list them in a manifest file. Small pieces let the player switch quality between segments and start playback quickly.
Why it matters
Segment length shapes how fast a video starts, how quickly quality can change and how much delay live viewers see. Short segments help live latency and switching but add more requests and overhead for the CDN. Getting this setting wrong shows up directly as slow starts, buffering or live streams that lag behind the action.
How it works
- Each rendition is cut into short files at keyframes, often every 2 to 6 seconds.
- A manifest lists the segments in order with their durations and addresses.
- The player downloads a few segments ahead to build a buffer before playback starts.
- Between segments, the player can switch to a different rendition if the network changes.
What is the best segment length for HLS?
Six seconds is the common default for HLS, because Apple's authoring guidance recommends a 6 second target duration. Shorter segments, such as 2 seconds, help live streams cut delay and let quality adapt faster. They also mean more requests and slightly worse compression. For on-demand libraries, 4 to 6 seconds is a reasonable balance.
Does segment length affect latency?
Yes, segment length strongly affects live latency, because players usually wait for several segments before starting. With 6 second segments and a buffer of three, viewers can sit 18 seconds or more behind live. This is one reason standard HLS often runs 10 to 30 seconds behind. Low-latency HLS adds smaller partial segments to bring delay down to roughly 2 to 5 seconds. For live sports or live shopping, where viewers should not learn the result from social media first, FastPix delivers live streams as LL-HLS.
Where it's used
Live sports streamers and OTT services split video into short segments so viewers can start watching right away and quality can change mid-stream without stopping.
Where it usually goes wrong, and how FastPix handles it
Slow segment downloads are hard to spot from the server side, so teams see buffering complaints without knowing whether the CDN, the network or the segment size is at fault.
Every segment request feeds FastPix Video Data, which reports request latency (average and maximum) and throughput per view, broken down by CDN, region, ISP and device. When buffering complaints arrive, your team can point to the CDN, ISP or region at fault with data.
By the numbers
- Apple's HLS authoring guidance states that target segment durations should be 6 seconds. (HLS Authoring Specification for Apple Devices)
- Apple's HLS authoring guidance states that keyframes (IDRs) should be present every two seconds. (HLS Authoring Specification for Apple Devices)
