Regression in calculating live edge in 2.x vs 1.6.x

[johanhil]

I have a Manifest that looks something like this:

<?xml version="1.0" encoding="utf-8"?>
<!-- Created with Unified Streaming Platform(version=1.7.19) -->
<MPD
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns="urn:mpeg:dash:schema:mpd:2011"
  xsi:schemaLocation="urn:mpeg:dash:schema:mpd:2011 http://standards.iso.org/ittf/PubliclyAvailableStandards/MPEG-DASH_schema_files/DASH-MPD.xsd"
  type="dynamic"
  availabilityStartTime="1970-01-01T00:00:00Z"
  publishTime="2016-08-17T14:36:56.591341Z"
  minimumUpdatePeriod="PT8S"
  timeShiftBufferDepth="PT27H6M44S"
  maxSegmentDuration="PT5S"
  minBufferTime="PT12S"
  profiles="urn:mpeg:dash:profile:isoff-live:2011,urn:com:dashif:dash264">
  <Period
    id="1"
    start="PT0S">
    <BaseURL>dash/</BaseURL>
    <AdaptationSet
      group="1"
      contentType="audio"
      lang="sv"
      minBandwidth="128000"
      maxBandwidth="128000"
      segmentAlignment="true"
      audioSamplingRate="48000"
      mimeType="audio/mp4"
      codecs="mp4a.40.2">
      <AudioChannelConfiguration
        schemeIdUri="urn:mpeg:dash:23003:3:audio_channel_configuration:2011"
        value="2">
      </AudioChannelConfiguration>
      <SegmentTemplate
        timescale="48000"
        initialization="vsh-$RepresentationID$.dash"
        media="vsh-$RepresentationID$-$Time$.dash">
        <!-- 2016-08-16T11:29:58.309333Z / 1471346998 - 2016-08-17T14:36:45.904000Z -->
        <SegmentTimeline>
          <S t="70624655918848" d="192512" r="24336" />
        </SegmentTimeline>
      </SegmentTemplate>
      <Representation
        id="svenska=128000"
        bandwidth="128000">
      </Representation>
    </AdaptationSet>
    <AdaptationSet
      group="2"
      contentType="video"
      par="16:9"
      minBandwidth="500000"
      maxBandwidth="4500000"
      minWidth="480"
      maxWidth="1280"
      minHeight="270"
      maxHeight="720"
      minFrameRate="25"
      maxFrameRate="50"
      segmentAlignment="true"
      mimeType="video/mp4"
      startWithSAP="1">
      <Representation
        id="video=500000"
        bandwidth="500000"
        width="480"
        height="270"
        frameRate="25"
        codecs="avc1.4D4015"
        scanType="progressive">
        <SegmentTemplate
          timescale="25"
          initialization="vsh-$RepresentationID$.dash"
          media="vsh-$RepresentationID$-$Time$.dash">
          <!-- 2016-08-16T11:29:58Z / 1471346998 - 2016-08-17T14:36:42Z -->
          <SegmentTimeline>
            <S t="36783674950" d="100" r="24400" />
          </SegmentTimeline>
        </SegmentTemplate>
      </Representation>
      <Representation
        id="video=1000000"
        bandwidth="1000000"
        width="640"
        height="360"
        frameRate="25"
        codecs="avc1.4D401E"
        scanType="progressive">
        <SegmentTemplate
          timescale="25"
          initialization="vsh-$RepresentationID$.dash"
          media="vsh-$RepresentationID$-$Time$.dash">
          <!-- 2016-08-16T11:29:58Z / 1471346998 - 2016-08-17T14:36:42Z -->
          <SegmentTimeline>
            <S t="36783674950" d="100" r="24400" />
          </SegmentTimeline>
        </SegmentTemplate>
      </Representation>
      <Representation
        id="video=1800000"
        bandwidth="1800000"
        width="960"
        height="540"
        frameRate="25"
        codecs="avc1.4D401F"
        scanType="progressive">
        <SegmentTemplate
          timescale="25"
          initialization="vsh-$RepresentationID$.dash"
          media="vsh-$RepresentationID$-$Time$.dash">
          <!-- 2016-08-16T11:29:58Z / 1471346998 - 2016-08-17T14:36:42Z -->
          <SegmentTimeline>
            <S t="36783674950" d="100" r="24400" />
          </SegmentTimeline>
        </SegmentTemplate>
      </Representation>
      <Representation
        id="video=3000000"
        bandwidth="3000000"
        width="1280"
        height="720"
        frameRate="25"
        codecs="avc1.4D401F"
        scanType="progressive">
        <SegmentTemplate
          timescale="25"
          initialization="vsh-$RepresentationID$.dash"
          media="vsh-$RepresentationID$-$Time$.dash">
          <!-- 2016-08-16T11:29:58Z / 1471346998 - 2016-08-17T14:36:42Z -->
          <SegmentTimeline>
            <S t="36783674950" d="100" r="24400" />
          </SegmentTimeline>
        </SegmentTemplate>
      </Representation>
      <Representation
        id="video=4500000"
        bandwidth="4500000"
        width="1280"
        height="720"
        frameRate="50"
        codecs="avc1.640020"
        scanType="progressive">
        <SegmentTemplate
          timescale="50"
          initialization="vsh-$RepresentationID$.dash"
          media="vsh-$RepresentationID$-$Time$.dash">
          <!-- 2016-08-16T11:29:58Z / 1471346998 - 2016-08-17T14:36:42Z -->
          <SegmentTimeline>
            <S t="73567349900" d="200" r="24400" />
          </SegmentTimeline>
        </SegmentTemplate>
      </Representation>
    </AdaptationSet>
  </Period>
</MPD>

I downloaded it at at 14:36:56, and looking at the segments available for the stream with id video=4500000, my last video segment ends at 14:36:38 (73567349900 / 50 + (200/50)*24400 = 1471444598).

In Shaka 1.6.x, this stream plays as expected, but in Shaka 2 it will calculate live edge as being after 14:36:38, meaning the stream does not start until a few seconds have passed and the encoder spits out a segment that is at the live edge.

On the demos for 1.6.3 and for 2.0.0-beta3, this is quite apparent.

My initial findings points to the live edge in 1.6 being calculated using computeStreamLimits_ in stream_video_source, which looks at the segments.
In 2.x, the live edge seems to be calculated by getLiveEdge_ which doesn't take the last segment end time into account.

This particular manifest has quite a big time shift buffer, but I can reproduce with a time shift buffer of less than an hour, so it's unrelated as far as I can tell.

I tried writing a unit test, but I did not get very far, sorry.

Is this a problematic manifest that just happened to work on 1.6, or a regression between 1.6 and 2.0?

I can provide links so that you can test this locally, just email me at [email protected]

[TheModMaker]

There are two problems here:

First, we do not account for suggestedPresentationDelay when determining where to start playing. So we want to play too close to the live edge and have to buffer until the segments become available. This has just been fixed on master.

Second, your manifest does not have a suggestedPresentationDelay. This means we use a default value of 5 seconds, which is too small for your setup. You should add a suggestedPresentationDelay attribute to your MPD element with about 20 seconds.

[joeyparrish]

Since the regression (suggestedPresentationDelay) was fixed, I'm closing the issue.

@johanhil, let us know if there's anything else we can do for you.