# DASH manifest types
<a name="dash-manifest-types"></a>

Dynamic Adaptive Streaming over HTTP (DASH) uses a Media Presentation Description (MPD) manifest to deliver streaming content. Understanding the structure and components of DASH manifests is essential for configuring and troubleshooting MediaTailor workflows.

MPD (Media Presentation Description)  
The MPD is the primary manifest file in DASH streaming that describes the structure and availability of media content. It contains information about periods, adaptation sets, representations, and segments that make up the streaming content.  
This manifest type is also known by several other names in various contexts:  
+ DASH manifest
+ DASH MPD
+ Master manifest (when comparing to HLS)
+ Presentation manifest
In MediaTailor workflows, the MPD is the entry point for playback requests and is where ad personalization begins.  

**Example MPD manifest example**  

```
<?xml version="1.0" encoding="UTF-8"?>
<MPD xmlns="urn:mpeg:dash:schema:mpd:2011" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="urn:mpeg:dash:schema:mpd:2011 DASH-MPD.xsd" profiles="urn:mpeg:dash:profile:isoff-live:2011" type="dynamic" minBufferTime="PT5.000S" maxSegmentDuration="PT2.005S" availabilityStartTime="2020-01-01T00:00:00Z" publishTime="2020-01-01T12:30:00Z" minimumUpdatePeriod="PT2.000S" timeShiftBufferDepth="PT5M">
  <Period id="1" start="PT0.000S">
    <AdaptationSet id="1" contentType="video" segmentAlignment="true" bitstreamSwitching="true" frameRate="30000/1001" maxWidth="1920" maxHeight="1080" par="16:9">
      <Representation id="1" mimeType="video/mp4" codecs="avc1.640028" width="1920" height="1080" bandwidth="5000000">
        <SegmentTemplate timescale="90000" initialization="init-stream$RepresentationID$.m4s" media="chunk-stream$RepresentationID$-$Number%05d$.m4s" startNumber="1" duration="180000"/>
      </Representation>
      <Representation id="2" mimeType="video/mp4" codecs="avc1.4d401f" width="1280" height="720" bandwidth="2800000">
        <SegmentTemplate timescale="90000" initialization="init-stream$RepresentationID$.m4s" media="chunk-stream$RepresentationID$-$Number%05d$.m4s" startNumber="1" duration="180000"/>
      </Representation>
      <Representation id="3" mimeType="video/mp4" codecs="avc1.4d401e" width="640" height="360" bandwidth="1100000">
        <SegmentTemplate timescale="90000" initialization="init-stream$RepresentationID$.m4s" media="chunk-stream$RepresentationID$-$Number%05d$.m4s" startNumber="1" duration="180000"/>
      </Representation>
    </AdaptationSet>
    <AdaptationSet id="2" contentType="audio" segmentAlignment="true" lang="eng">
      <Representation id="4" mimeType="audio/mp4" codecs="mp4a.40.2" audioSamplingRate="48000" bandwidth="128000">
        <SegmentTemplate timescale="48000" initialization="init-stream$RepresentationID$.m4s" media="chunk-stream$RepresentationID$-$Number%05d$.m4s" startNumber="1" duration="96000"/>
      </Representation>
    </AdaptationSet>
  </Period>
</MPD>
```

Period  
A Period is a temporal section of a DASH presentation. Each Period contains one or more adaptation sets and represents a span of media time. In ad insertion workflows, separate Periods are typically used to delineate between content and ads.  
This component is also known by several other names:  
+ Content segment
+ Timeline section
+ Program segment
In MediaTailor workflows, Periods are used to separate main content from ad content, with each ad typically represented by its own Period.  

**Example Period example**  

```
<Period id="ad-period-1" start="PT30.000S" duration="PT15.000S">
  <AdaptationSet id="1" contentType="video" segmentAlignment="true" bitstreamSwitching="true" frameRate="30000/1001" maxWidth="1920" maxHeight="1080" par="16:9">
    <Representation id="1" mimeType="video/mp4" codecs="avc1.640028" width="1920" height="1080" bandwidth="5000000">
      <SegmentTemplate timescale="90000" initialization="ad1/init-stream$RepresentationID$.m4s" media="ad1/chunk-stream$RepresentationID$-$Number%05d$.m4s" startNumber="1" duration="180000"/>
    </Representation>
  </AdaptationSet>
</Period>
```

AdaptationSet  
An AdaptationSet groups a set of interchangeable encoded versions of one or several media content components. For example, one AdaptationSet might contain multiple video quality levels, while another might contain multiple audio language options.  
This component is also known as:  
+ Media component group
+ Stream set
+ Track group
In MediaTailor workflows, AdaptationSets are preserved during ad insertion to maintain consistent media types between content and ads.

Representation  
A Representation is a specific encoded version of the media content within an AdaptationSet. Each Representation typically differs in bitrate, resolution, or other encoding parameters, allowing clients to select the most appropriate version based on network conditions and device capabilities.  
This component is also known as:  
+ Rendition (similar to HLS)
+ Quality level
+ Bitrate variant
+ Stream variant
In MediaTailor workflows, Representations in ad Periods are matched as closely as possible to the Representations in content Periods to ensure a smooth viewing experience.

Segment  
A Segment is a unit of media data that can be referenced individually by a URL. Segments contain the actual media content (video, audio, etc.) and are referenced within the MPD. There are two main types of segments in DASH:  
+ **Initialization Segment**: Contains initialization information for a Representation, such as codec parameters and timing information.
+ **Media Segment**: Contains the actual media data for a specific time range within a Representation.
In MediaTailor workflows, segment URLs are often modified to point to the appropriate content or ad media files.

**Note**  
DASH manifests are XML-based files that typically use the `.mpd` extension. The terminology for these files and their components may vary across different documentation and contexts, but the fundamental structure remains the same in the DASH streaming architecture.

When configuring MediaTailor, you provide the URL to the MPD manifest in your content origin. MediaTailor then handles the personalization of the manifest, typically by inserting additional Periods for ads according to your configuration.

For more information about DASH manifest specifications, see the [DASH Industry Forum Implementation Guidelines](https://dashif.org/docs/DASH-IF-IOP-v4.3.pdf).

# Advanced DASH manifest concepts
<a name="dash-manifest-advanced-concepts"></a>

When working with DASH manifests in MediaTailor, understanding the following advanced concepts can help you configure and troubleshoot your streaming workflows more effectively:

Period start time calculation  
In DASH manifests, Period start times are calculated based on the MPD's `availabilityStartTime` attribute and the Period's `start` attribute. For live streams, the start time is relative to the availability start time, while for VOD content, it's typically relative to the beginning of the presentation.  
When MediaTailor inserts ad Periods, it carefully calculates the start times to ensure seamless transitions between content and ads. This calculation takes into account:  
+ The original Period's start time
+ The duration of preceding ad Periods
+ Any time offset specified in the ad decision server response

Preroll timing calculations  
Preroll ads in DASH manifests require special handling because they appear before the main content begins. MediaTailor inserts preroll ads as separate Periods at the beginning of the manifest with appropriate start times and durations.  
For preroll ads, MediaTailor:  
+ Creates a new Period for each preroll ad
+ Sets the first preroll Period's start time to 0
+ Adjusts the start time of the main content Period to account for the total duration of all preroll ads

Live-to-VOD transitions  
DASH manifests can transition from live to VOD (Video on Demand) format when a live stream ends. This transition involves changing the MPD's `type` attribute from `dynamic` to `static` and adjusting other attributes like `timeShiftBufferDepth` and `minimumUpdatePeriod`.  
When MediaTailor processes manifests during live-to-VOD transitions, it ensures that:  
+ Ad markers are preserved in the VOD manifest
+ Period start times are adjusted to maintain proper timing
+ The manifest remains compatible with VOD playback clients

DRM handling  
Digital Rights Management (DRM) information in DASH manifests is typically included in the `ContentProtection` elements within AdaptationSets or Representations. MediaTailor preserves these elements during ad insertion to ensure that content protection remains intact.  
When processing DRM-protected content, MediaTailor:  
+ Maintains all ContentProtection elements from the original manifest
+ Ensures that ad content uses compatible DRM schemes if applicable
+ Preserves any DRM-related attributes and elements throughout the manifest

SCC flags  
Supplemental Content Control (SCC) flags in DASH manifests provide additional information about content characteristics and playback requirements. These flags are typically included as attributes or elements within the MPD structure.  
Common SCC flags that MediaTailor processes include:  
+ Content rating information
+ Accessibility features (closed captions, audio descriptions)
+ Content advisory notices
+ Playback restrictions
MediaTailor preserves these flags during manifest processing to ensure that all content metadata is maintained in the personalized manifest.

Understanding these advanced concepts helps you configure MediaTailor for optimal performance and troubleshoot any issues that may arise in your DASH streaming workflows.