duration Attribute in the SegmentTemplate - AWS Elemental MediaPackage
How it worksLimitationsWith compact manifests

duration Attribute in the SegmentTemplate

In a default DASH manifest, SegmentTemplate holds a SegmentTimeline. The timeline describes all the segments in Representation, including their duration and their start time. With live events, AWS Elemental MediaPackage adds segments to the timeline as it receives them from your encoder. To be aware of newly available segments, the playback device must regularly request an updated manifest from MediaPackage.

If all the segments in a representation have the same duration, you can help to reduce latency and shorten the manifest by enabling MediaPackage to remove the SegmentTimeline objects. In their place, MediaPackage adds a duration attribute to the SegmentTemplate properties. The playback device calculates when segments are available by using duration and startNumber. Because the playback device doesn't have to rely on an updated manifest to know about segments, it doesn't have to constantly request updates to maintain playback. For information about how the duration attribute works, see the following sections.

Topics

How the duration attribute works

Enable the $duration$ attribute through the Segment template format setting on the DASH endpoint, as described in Creating a DASH endpoint. This is what happens with the manifest:

  1. When AWS Elemental MediaPackage generates the DASH manifest, it adds the duration attribute to the SegmentTemplate object, as shown in the following example:

    <SegmentTemplate timescale="30000" media="index_video_1_0_$Number$.mp4?m=1535562908" initialization="index_video_1_0_init.mp4?m=1535562908" startNumber="175032" duration="90000" presentationTimeOffset="62061"/>

    A segment timeline and individual segment descriptions are not included in the segment template.

    Important

    Except for the final segment, segments must be no more than 50% deviation from the value of the duration. With a 90000 duration, segments must be between 45000 and 135000 (1.5 to 4.5 seconds with a 30000 timescale).

    The following is an example of an adaptation set that uses the duration in the segment template:

    <AdaptationSet mimeType="video/mp4" segmentAlignment="true" subsegmentAlignment="true" startWithSAP="1" subsegmentStartsWithSAP="1" bitstreamSwitching="true">
  <Representation id="1" width="852" height="480" frameRate="30/1" bandwidth="1200000" codecs="avc1.4D401F">
    <SegmentTemplate timescale="30000" media="index_video_1_0_$Number$.mp4?m=1535562908" initialization="index_video_1_0_init.mp4?m=1535562908" startNumber="175032" duration="90000" presentationTimeOffset="62061"/>
  </Representation>
  <Representation id="2" width="640" height="360" frameRate="30/1" bandwidth="800000" codecs="avc1.4D401E">
    <SegmentTemplate timescale="30000" media="index_video_3_0_$Number$.mp4?m=1535562908" initialization="index_video_3_0_init.mp4?m=1535562908" startNumber="175032" duration="90000" presentationTimeOffset="62061"/>
  </Representation>
  <Representation id="3" width="320" height="240" frameRate="30/1" bandwidth="499968" codecs="avc1.4D400D">
    <SegmentTemplate timescale="30000" media="index_video_5_0_$Number$.mp4?m=1535562908" initialization="index_video_5_0_init.mp4?m=1535562908" startNumber="175032" duration="90000" presentationTimeOffset="62061"/>
  </Representation>
</AdaptationSet>

  2. The playback device requests segments using the URL that's defined in the media attribute. In the URL, it replaces the $Number$ variable with the number of the segment, starting with the value of the startNumber in the SegmentTemplate for the first segment.

  3. If your playback device needs to determine the most recent segment, it uses this formula:

    ((wall clock time - availabilityStartTime ) / (duration / timescale )) + startNumber

    A playback device is calculating the most recent segment with the following values:

    • Wall clock time from the playback device: 2018-11-16T19:18:30Z

    • availabilityStartTime - Attribute from the MPD object of the manifest: 2018-11-16T19:08:30Z

    • duration - Attribute from the SegmentTemplate object of the manifest: 90000

    • timescale - Attribute from the SegmentTemplate: 30000

    • startNumber - Attribute from the SegmentTemplate: 175032

    The calculation it uses is ((2018-11-16T19:18:30Z - 2018-11-16T19:08:30Z) / (90000/30000)) + 175032

    This calculation then becomes (600 seconds elapsed time) / (3 second segment durations) = 200 elapsed segments. Adding those segments to the 175032 start segment makes the most recent segment 175232.

duration Attribute limitations

To ensure proper playback and help prevent issues with conflicting segment durations, AWS Elemental MediaPackage enforces the following limitations for the duration attribute:

  • You can enable the feature only when you create the endpoint.

    You can't modify the endpoint to later add the duration attribute to your DASH manifests. This includes changing from one segment template format to one that uses duration. For example, you can't create an endpoint that uses the $Time$ variable with SegmentTimeline, and then edit the endpoint to use the $Number$ variable with duration.

  • You must keep the segment duration value that you set when you create the endpoint.

    You can't edit the endpoint to modify the segment duration.

  • You must produce single period DASH manifests from endpoints that use duration.

    You can't use multi-period DASH with the duration attribute.

  • Your ingest stream must use a regular segmentation cadence.

  • You can't use variable segment length in the ingest stream. For example, resulting of a SCTE-35-related segmentation.

duration Attribute with compacted DASH manifests

Combining compacted manifests with the duration attribute will further reduce the size of the manifest, but not by much. Compacted manifests have one SegmentTemplate and SegmentTimeline per adaptation set. When you use the duration attribute, AWS Elemental MediaPackage removes the segment timeline. With both treatments, the manifest has one SegmentTemplate per adaptation set, and no SegmentTimeline. See the following examples.

For more information about compacted manifests, see Compacted DASH manifests.

Important

If the segments in a representation intentionally have varying sizes of segments, don't use the duration attribute. This treatment works only when the segments are a consistent size.

The following is an example of a compacted manifest:
<AdaptationSet mimeType="video/mp4" segmentAlignment="true" subsegmentAlignment="true" startWithSAP="1" subsegmentStartsWithSAP="1" bitstreamSwitching="true">
   <SegmentTemplate timescale="30000" media="index_video_$RepresentationID$_0_$Number$.mp4?m=1543947824" initialization="index_video_$RepresentationID$_0_init.mp4?m=1543947824" startNumber="1">
     <SegmentTimeline>
       <S t="62000" d="60000" r="9"/>
     </SegmentTimeline>
   </SegmentTemplate>
   <Representation id="1" width="640" height="360" frameRate="30/1" bandwidth="749952" codecs="avc1.640029"/>
   <Representation id="2" width="854" height="480" frameRate="30/1" bandwidth="1000000" codecs="avc1.640029"/>
   <Representation id="3" width="1280" height="720" frameRate="30/1" bandwidth="2499968" codecs="avc1.640029"/>
</AdaptationSet>
The following is an example of a compacted manifest with the duration attribute:
<AdaptationSet mimeType="video/mp4" segmentAlignment="true" subsegmentAlignment="true" startWithSAP="1" subsegmentStartsWithSAP="1" bitstreamSwitching="true">
   <SegmentTemplate timescale="30000" media="index_video_$RepresentationID$_0_$Number$.mp4?m=1543947824" initialization="index_video_$RepresentationID$_0_init.mp4?m=1543947824" startNumber="1" duration="60000"/>
   <Representation id="1" width="640" height="360" frameRate="30/1" bandwidth="749952" codecs="avc1.640029"/>
   <Representation id="2" width="854" height="480" frameRate="30/1" bandwidth="1000000" codecs="avc1.640029"/>
   <Representation id="3" width="1280" height="720" frameRate="30/1" bandwidth="2499968" codecs="avc1.640029"/>
</AdaptationSet>