Error adding external ttml captions file after load.

[ewosleger]

Shaka v2.0.8
We noticed Shaka is displaying our captions in reverse order from our embedded ttml files in the manifest:
"jumped over the fence"
"Quick brown fox"

We have external caption files also so I am trying to addTextTrack() to the player:
player.load(_globalSelf.manifest).then(function() {
parent.messageService.dispatch(ShoMediaNotifications.PLAYER_READY, null);
if(typeof parent.params.dash_ttml !== 'undefined'){

  this.player.addTextTrack(parent.params.dash_ttml, 'eng','caption','text/ttml');
}

}).catch(_globalSelf.onError);

player errors out: tb[b] is not a constructor.

[ewosleger]

Regarding our captions in reverse order. A snippet of a specific ttml segment.
<p begin="00:00:55.000" end="00:00:56.541" region="pop1" style="basic" tts:extent="45% 5.33%" tts:origin="27.5% 79.33%"> JEANNIE: <span tts:fontStyle="italic">You still</span> </p> <p begin="00:00:55.000" end="00:00:56.541" region="pop2" style="basic" tts:extent="67.5% 5.33%" tts:origin="15% 84.66%"> <span tts:fontStyle="italic">stubbornly insist on being</span> </p>

The first <p> "pop1" tss:origin y cord is 79.33% from the top.
The secons <p> "pop2" tss:origin y cord should be below "pop1" y at 84.66% however it is rendering above the first <p>.

[ismena]

Hi @ewosleger,
Please correct me if I misunderstood: looks like you are reporting 2 separate issues:

1. Captions showing up in reverse order
2. External text track not being loaded
   Is that right?

Regarding the first one (captions in reverse order), could you tell me if the 'tts:writingMode' attribute is present on the segment and what it's value is if yes.

[ewosleger]

Yes, one issue lead to another. We are experiencing the reverse stacking of the captions. Looking for a quick solution we have an addition ttml files that is not bundled with the manifest the we wanted to load in addition to the embedded ttml files.

In the player.load i added the snippet:
`player.load(_globalSelf.manifest).then(function() {
parent.messageService.dispatch(ShoMediaNotifications.PLAYER_READY, null);
if(typeof parent.params.dash_ttml !== 'undefined){

this.player.addTextTrack(parent.params.dash_ttml, 'eng','caption', 'text/ttml');
}

}).catch(_globalSelf.onError);`

Assuming that is the correct addTextTrack syntax, I was thrown the following error:
'player errors out: tb[b] is not a constructor'

[TheModMaker]

Have you tried with the latest master or the latest release? Does the error occur with the demo app? With the demo site, you can just load your manifest and run the following code in the JavaScript console:

shakaDemo.localPlayer_.addTextTrack('yourUrl', 'eng', 'caption', 'text/ttml');

Are all the captions the same type? If the external captions are TTML and the manifest ones are VTT or TTML in MP4, then we will error out in that version. We don't support switching between text track formats until v2.1.

Also, the code you posted may not work because you don't use bind. The nested function uses this, which will be window at that time. To work, you need to do something like this (though the error won't cause the errors you see):

player.load(...).then(function() {
  ...
}.bind(this));

As for the out of order lines, this is partially a browser problem. We just take the cues and create VTTCue objects and pass to the browser. When the browser displays cues that have overlapping times, it displays them on top of each other in reverse add order. That may be why they appear like that. I don't know if we support the offset attributes nor how the browser will render them.

[ismena]

@ewosleger I might be able to help with the ordering if you could tell me if the 'tts:writingMode' attribute is present on the segment and what it's value is if yes.

[ewosleger]

We do not have the attribute "tts:writingMode" in our ttml.

[ewosleger]

I believe out latest build version is Shake v 2.0.8 - I will update and test latest stable build.

[ismena]

I verified that we are parsing the "tts:origin" attribute and constructing the VttCues correctly, so it might be a bug on the browser's side as @TheModMaker mentioned.
Is this happening in a particular browser?

[joeyparrish]

Let's split the caption ordering into a separate bug report. Here we will deal with the more severe issue of an API failing in compiled mode.

[joeyparrish]

Even in uncompiled mode, the error is easily reproducible on the nightly and in v2.1.2:

https://nightly-dot-shaka-player-demo.appspot.com/demo/#asset=//ams-samplescdn.streaming.mediaservices.windows.net/11196e3d-2f40-4835-9a4d-fc52751b0323/TearsOfSteel_WAMEH264SmoothStreaming720p.ism/manifest(format=mpd-time-csf);play

Assertion failed: Inconsistent active stream
Uncaught exception in event handler TypeError: Cannot read property 'language' of undefined

It does not reproduce in v2.0.9.

[joeyparrish]

We broke this in 6b6bfb7

[joeyparrish]

Let's unpack several issues mentioned here.

Exception in addTextTrack

The exception you get ("tb[b]" etc), is caused by you passing the wrong MIME type. "text/ttml" is not the official MIME type of TTML, so our parser is not selected. Please use "application/ttml+xml" instead.

Display order for overlapping cues

We don't control this directly. Cues are displayed by the browser. I've split this into #848.

Exception in demo app

There is an exception in the demo app UI that prevents the UI from being updated correctly with the list of tracks. This is caused by an unexpected situation in which text tracks exist, but none are marked as "active" tracks when we hit shakaDemo.updateLanguageOptions_(). This is triggered by the Tears of Steel demo link above.

I thought this was the same error as the addTextTrack() exception in the original report, but it is not. There is also no difference here in compiled/uncompiled mode.

If we fix this exception in the demo, the UI is populated correctly and the text tracks can be manually selected, but none is selected for us by the player. So this doesn't really fix the root of the problem, which is that the Player fails to select the newly-added tracks.

This regression started in 6b6bfb7.