The ceiling and the individual durations
EXTINF gives the duration of the following media segment. EXT-X-TARGETDURATION is a playlist-level integer in seconds. Under RFC 8216, each EXTINF duration rounded to the nearest integer must fit within that target. A target of six does not mean every segment lasts exactly six seconds.
A short final segment, a production boundary or the encoder's timing can produce different durations. Consequently, multiplying a segment count by the target is only an estimate. Reading the actual EXTINF values gives a better total when a support engineer needs the length of the visible playlist window.
A worked window calculation
Consider five hypothetical segments lasting 5.96, 6.02, 5.98, 6.00 and 3.04 seconds. Their total is 27.00 seconds. Multiplying five by a six-second target would instead suggest 30 seconds, overstating the published media by three seconds. The difference matters when explaining a short seek-back range.
This total still is not the player's buffer. A player may have downloaded only part of the listed window, may be playing some seconds behind its end, or may retain earlier downloaded data. Describe the calculated quantity as playlist duration rather than buffered duration.
How timing becomes a delivery question
If a six-second segment needs eight seconds to download repeatedly, the player consumes media faster than that transfer supplies it. One isolated slow transfer may be absorbed by previously buffered content; repeated slow transfers can exhaust that reserve. Duration and transfer time must therefore be recorded separately.
A short segment is not automatically a low-latency implementation. Publication cadence, player positioning, requests, decoding and rendering all contribute. A viewer cannot safely correct a publisher's segment timing by editing the target number in a local copy; that does not change the encoded media.
Questions about this guide
Is target duration the live delay?
No. It constrains media-segment timing. End-to-end live delay includes production, publication, transfer and playback choices.
Does every segment need the same duration?
No. Check individual EXTINF values and the applicable target-duration rule rather than assuming identical lengths.