Video on demand encoding (DASH)

Single-period MPEi-gno/re-dDASH manifest ^(Alpha)

Expectations for single-period MPEi-gno/re-dDASH manifest

Google DAI performs the following validations on the raw MPD.

Content requirements

DASH content must follow all the rules specified in the DASH-IF Interoperability Points.

MPEi-gno/re-dDASH

Google DAI performs the following validations and makes the following assumptions on the raw MPD.

1. MPD element validations:
   • @profiles is set to urn:mpeg:dash:profile:isoff-live:2011.
   • @type is set to static.
   • MPD has exactly one Period element.

   <MPD xmlns="urn:mpeg:dash:schema:mpd:2011" xmlns:xsi="http://w3.org/2001/XMLSchema-instance" xsi:schemaLocation="urn:mpeg:dash:schema:mpd:2011 DASH-MPD.xsd" type="static" profiles="urn:mpeg:dash:profile:isoff-live:2011" maxSegmentDuration="PT2S" minBufferTime="PT2S">

    <Period …>

    …

    </Period>

    …

   </MPD>

2. Period element validations:
   • Period has at least one @AdaptationSet element.
   • There must be at least one nested EventStream element with Event elements encoded with splice points for the period to be split. Reference SCTE-35 for the splice point encoding requirements.

   <Period id=”1” start="PT0S">

     <AdaptationSet …>

       …

     </AdaptationSet>

     <AdaptationSet …>

       …

     </AdaptationSet>

   </Period>

3. The following are required for AdaptationSet element validations.
   Ensure AdaptationSet has at least one @Representation element.
   Thumbnail and subtitle adaptation sets are supported. Subtitle adaptation sets are required.

   <AdaptationSet mimeType="video/mp4" startWithSAP="1" contentType="text" par="16:9" minWidth="640" maxWidth="640" minHeight="360" maxHeight="360" maxFrameRate="60/2" segmentAlignment="true">

     <Role schemeIdUri="urn:mpeg:dash:role:2011" value="main"></Role>

     <ContentComponent id="0" contentType="video" />

     <Representation …>

       …

     </Representation>

     <Representation …>

       …

     </Representation>

   </AdaptationSet>

4. Complete Representation element validations:
   • Ensure @id is non-empty.
   • There must not be @SegmentBase or @SegmentList elements.

   <Representation width="640" height="360" sar="1:1" frameRate="60/2" codecs="avc1.64001e" id="V300" bandwidth="300000">

     …

   </Representation/>

5. Validate SegmentTemplate with $Time$:
   • Ensure SegmentTemplate elements contain a nested SegmentTimeline element for explicit addressing of media segments.
   • SegmentTimeline S elements may contain the S@t attribute, which is used for media URLs.
     • If not provided, the value is assumed to be 0 for the first S element and for subsequent S elements, the value shall be assumed to be the sum of the previous S element's earliest presentation time and contiguous duration (that is, previous S@t + @d * (@r + 1)).
     • SegmentTemplate@startNumber is not used.

     <SegmentTemplate timescale="90000" initialization="$RepresentationID$/init.mp4" media="$RepresentationID$/$Time$.m4s">

       <SegmentTimeline>

         <S t="0" d="270000" r="20" />

       </SegmentTimeline>

     </SegmentTimeline>

6. Google DAI supports the time component part of the ISO-8601 duration and supports the optional integer day component: P0Y0M[n]DT[n]H[n]M[n]S. The days component is converted to a duration by considering 1 day = 24 hours and is added to the time component. Nanosecond is the lowest granularity that we recognize.

Valid format examples:

• P0Y0M
• P0Y0M2D
• P2D
• PT3H
• PT0H3M
• P0Y0M0DT0H0M1.000S
• P0Y0M1DT2H4M10S
• PT0.000000001S

Invalid format examples:

• P
• PT
• 2007-03-01
• P5Y0M1DT2H4M1.000S
• P0Y1.5M1DT2H4M1.000S
• P0YiM1DT2H4M1.000S
• P0Y0M.3DT0H0M1.000S
• 3h
• PT100,000H

Subtitles

1. Google DAI supports both TTML and WebVTT formatted subtitles.
2. Google DAI supports all sidecar subtitle files provided through the MRSS feed.
3. Sidecar subtitle files specified in the DASH manifest will not be converted and will not be present in the conditioned manifest. If sidecar subtitles are required, they must be specified via the MRSS feed.

Unsupported DASH manifest sidecar subtitles

4. Fragmented subtitles specified in an AdaptationSet with contentType="text", and with a SegmentTimeline are supported, but subtitle segments will also need to have their segment boundaries aligned with the splice point markers to pass validation.
   Note: Roku devices don't support fragmented segments in an AdaptationSet.

Supported DASH manifest fragmented subtitles

SCTE-35

1. Google DAI will only recognize splice points as SCTE-35 markers carried in DASH MPD@Period@EventStream@Event elements if they pass the following validations:
   • Base64 encoded SCTE-35 data must be contained in the Event@Signal@Binary element.
     Only splice_insert is supported.
   • EventStream elements containing Events with SCTE-35 markers must have @schemeIdUri set to urn:scte:scte35:2014:xml+bin.
   • EventStream@timescale must be set or it will be assumed to be set to 1 (seconds timescale).
   • Event@presentationTime must be set on each Event element.
   • Event@Signal@namespace must have namespace http://scte.org/schemas/35/2016.
   • Events in the EventStream must be in sorted order by Event@presentationTime.
2. Splice_insert assumptions
   All splice_insert markers in the EventStream will be treated as ad break placement opportunities, that is, single-period conditioning does not differentiate between cue-outs and cue-ins, and instead treats any signal as an ad break placement opportunity.
3. Google DAI for DASH VOD does not support splitting segments and therefore only allows a 100 ms tolerance for how far a splice point's presentation time can be from the closest segment boundary.