HLS Target Duration

A common issue when playing live HLS is the value of target duration (EXT-X-TARGETDURATION). The target duration is an integral number of seconds that correspond to the longest segment in the stream. Depending on HLS version, this value must either be higher than the longest duration, or can be rounded to the closest integer, but many players desire a lower value in order to work best. This is due to that the target-duration value influences how often the client can ask for a playlist update.

Because live ingest node (ESB3003) generates segments with a precise average segment duration, adjusted segmentation boundaries due to SCTE-35 ad markers number may result in a single segment duration being 1.5 times the average duration. These singular values then effect the target-duration to become high.

To be able to fine-tune the target duration, the ew-manip service has an option to change the #EXT-X-TARGET-DURATON value by using the special query-string trigger target-duration= once ew-manip has been triggered with the general ewm=1 trigger.

An example of a request that includes the target-duration=5 query parameter to set #EXT-X-TARGET-DURATON to 5seconds could look like this:

http://repack-host/__cl/cg:live/__c/program/__op/default/__f/index.m3u8?ewm=1&target-duration=5

This will only apply to “live-like” playlists from the repackager. With “live-like” playlists, we mean playlists which come from a live channel including an interval in the past. Such playlists can be detected by searching for the part __cl/cg: in the URL that indicates that the URL is part of a live channel group. Media playlists with the stopTime in the past are technically VoD playlists, but since there is a transition from EVENT to VOD type of playlist as the stopTime is passed, they should be treated as live playlists.

For pure VoD assets, the target-duration can simply be calculated from the longest segment in the playlist, and there is in general no limit on how fast the segments can be requested, so there is no need for target duration modifications.