SegmentTemplate

SegmentTemplate is a component of the MPEG-DASH standard used to describe how to construct the URLs for media segments and the initialization segment for a given representation. It consolidates the rules for segment URLs into a single template, enabling dynamic generation of segment addresses during playback.

The element provides attributes such as media and initialization, along with timing-related settings like timescale, duration, startNumber, and an optional index. The media attribute specifies a URL template for the media segments, while initialization defines the template for the initialization segment. Timescale and duration define the segment timing in time units, and startNumber indicates the first segment number. An optional index attribute can reference an external segment index. SegmentTemplate may also contain a SegmentTimeline sub-element to express exact segment timings and durations.

SegmentTimeline offers a sequence of S elements, each describing a segment’s duration (d), start time (t), and an optional repeat count (r). This allows irregular segment durations or gaps to be represented precisely. When SegmentTimeline is present, its timing information supersedes fixed duration in the template, enabling complex segment pacing. In templates, clients substitute placeholders to form concrete URLs. Common placeholders include $Number$ for the segment index, $Time$ for the segment start time, and $Bandwidth$ and $RepresentationID$ for selecting the appropriate representation path. The resulting URLs are used to fetch media segments during streaming.

SegmentTemplate is typically placed within a Representation or Adaptation Set in a Media Presentation Description (MPD). It enables scalable, adaptive streaming by avoiding per-segment lists and providing a reusable scheme for segment retrieval across multiple representations or profiles.

See also: MPEG-DASH, MPD, SegmentTimeline, SegmentList.