media Attribute in SegmentTemplate - AWS Elemental MediaPackage
How it works

media Attribute in SegmentTemplate

The media attribute in the SegmentTemplate properties defines the URL where playback devices send segment requests. By default, this URL uses a $Number$ variable to identify the specific segment that's requested. When a playback device requests the segment, it replaces the variable with the number identifier of the segment. For the first segment in the representation, replace this identifier with the value of the startNumber from the SegmentTemplate properties. Each additional segment increments by one.

Some players navigate the segments better when the segments are identified instead by the timestamp for when playback is available. To support this use case, MediaPackage uses the $Time$ variable instead of $Number$ in the URL of the media attribute. When a playback device requests the segment, it replaces the variable with the availability start time of the segment. This start time is identified in the t value of the segment (S) properties in the SegmentTimeline object. For an example, see How It Works.

How the $Time$ variable works

Enable the $Time$ variable through the Segment template format setting on the DASH endpoint, as described in Creating a DASH endpoint. AWS Elemental MediaPackage takes the following actions:

  1. When MediaPackage generates the DASH manifest, it uses the $Time$ variable in the media value of the SegmentTemplate object, as shown in the following example:

    <SegmentTemplate timescale="30" media="index_video_1_0_$Time$.mp4?m=1122792372" initialization="index_video_1_0_init.mp4?m=1122792372" startNumber="2937928">

  2. When a playback device requests segments, it uses the URL defined in the media attribute and replaces the variable with the availability start time of the segment that's requested.

    Important

    The value that replaces the variable must be an exact t value of a segment. If the request uses an arbitrary timestamp, MediaPackage doesn't seek the closest segment.

    The following is an example of a segment template from a representation. It uses the $Time$ variable:

    <SegmentTemplate timescale="30000" media="155_video_1_2_$Time$.mp4?m=1545421124" initialization="155_video_1_2_init.mp4?m=1545421124" startNumber="710">
  <SegmentTimeline>
       <S t="255197799" d="360360" r="8"/>
       <S t="258441039" d="334334"/>
  </SegmentTimeline>
</SegmentTemplate>

    The request URL for the first segment is 155_video_1_2_255197799.mp4. With a 360360 duration, the next segment request is 155_video_1_2_255558159.mp4, and so on through the ninth segment.

    The final segment request is 155_video_1_2_258441039.mp4.