native text display fails to render nested TTML cues

Have you read the FAQ and checked for duplicate open issues? Yes

What version of Shaka Player are you using? 2.5.6

Can you reproduce the issue with our latest release version? Yes

Can you reproduce the issue with the latest code from master? Yes

Are you using the demo app or your own custom app? Custom app

If custom app, can you reproduce the issue using our demo app?

What browser and OS are you using? Chrome on a laptop, Tizen and WebOS

For embedded devices (smart TVs, etc.), what model and firmware version are you using? webOS 3.2-4.7 and Tizen 3-5

What are the manifest and license server URIs? Will be provided by email.

What did you do? Watched the video and sometimes the subtitles are not showing.

What did you expect to happen? The subtitles to be rendered.

What actually happened? The first and last paragraphs are rendered but the rest are not. The rendering works with the same manifest on version 2.5.5 but not on 2.5.6. Couldn’t see anything unusual on the logs.

<p begin="00:04:46.680" end="00:04:49.360" region="r0" style="p">
    Lorem ipsum dolor,<br/>
    consectetur adipisicing elit.
   </p>
   <p begin="00:05:25.560" end="00:05:29.240" region="r0" style="p">
    <span tts:fontStyle="italic">-Excepteur sint.</span><br/>
    <span tts:fontStyle="italic">-Duis aute.</span>
   </p>
   <p begin="00:05:33.360" end="00:05:36.040" region="r0" style="p">
    <span tts:fontStyle="italic">Excepteur sint...</span>
   </p>
   <p begin="00:05:36.200" end="00:05:39.800" region="r0" style="p">
    <span tts:fontStyle="italic">Aliquip ex ea commodo,</span><br/>
    <span tts:fontStyle="italic">Officia Deserunt.</span>
   </p>
   <p begin="00:05:41.520" end="00:05:44.520" region="r0" style="p">
    <span tts:fontStyle="italic">Mollit</span> Fugiat Nulla Pariatur?
   </p>

Possibly related to this https://github.com/google/shaka-player/pull/1962 ?

[joeyparrish]

I’ve updated the title of the issue to reflect the fact that this is a problem specifically for native text display. This does not yet support nested cues.

[joeyparrish]

SimpleTextDisplayer should iterate through nestedCues and flatten them out. This will not accurately represent TTML nested cues, but it will be as close as we can get with the VTTCue and TextTrackCue APIs in browsers today.