Cannot read property 'length' of null when try to enable captioning

[SemihGk]

Have you read the FAQ and checked for duplicate issues:

What version of Shaka Player are you using:
2.2 (reproduced 2.1.x as well)

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:
My custom app. I could not reproced the error on the demo app. Probably video contents in the demo app are not suitable for this error.

If custom app, can you reproduce the issue using our demo app:
No.

What browser and OS are you using:
Mac OS: 10.12.6
Chrome 60

What are the manifest and license server URIs:
(you can send the URIs to shaka-player-issues@google.com instead, but please use GitHub and the template for the rest)
If it's required, we can send the custom app.

What did you do?
Enabled captioning on and waited around a minute(time gap is unpredictable). Then, it caught the error when I tried to disable and enable again.

What did you expect to happen?
It should not throw an error.

What actually happened?
Video is stopped. Please check the screenshot. As you may see it in screenshot, It throws the error at lib/text/simple_text_displayer.js :231, cues.length . When 'cues' is null. I put a console.log to show it in screenshot as well.

[ismena]

Hi @SemihGk, thanks for reporting.

Having access to the app/content would definitely help us figure out what's going on. Feel free to send it to shaka-player-issues@google.com.

[SemihGk]

Thank you for your prompt response. I just sent the app with its instructions. Please let me know if you need more information.

[SemihGk]

I was testing the demo app and I could finally reproduce the error. Please check the screenshot:

Tested video: Sintel 4k (multicodec, VTT in MP4).

[joeyparrish]

Did you reproduce in the demo by turning captions on and off? Is it easier to reproduce in your own application than in the demo?

[SemihGk]

Yes, I turned captions on. Then, waited maybe 30 minutes. I replayed the video again and turned off and on several times. After these tries, I could reproduce it. It is definitely tough to reproduce in the demo. It is much easier to reproduce it in our app.

Edit: Reproduced again after I have done same steps, but this time video was not stopped.

[vaage]

A small update on this.

TextTrack.cues is only null when mode is set to "disabled". As we can see in the initial post, the current text track that the displayer is set to "disabled". This explains why we are getting a null list of cues.

What I am still looking into is why the track is being set to "disabled" in the first place. When toggling close captions on and off, the track is set to "hidden". So at some other point, someone is setting mode to "disabled".

[joeyparrish]

@SemihGk, is your application directly manipulating the track state instead of using Player.setTextTrackVisibility()? Are you using custom video controls (video.controls == false) or the built-in browser controls (video.controls == true)?

It is possible that the browser built-in controls use "disabled" instead of "hidden".

[SemihGk]

Thank you for your responses, @vaage and @joeyparrish.

We did not set the mode to "disabled" in our application. Everything is just default. Also, same error is reproduced in the demo app. I assume demo app do not have any custom settings as well. It only happens when we turn captions on and off without changing any settings(including built-in browser controls).

[vaage]

@joeyparrish You are right. Once we change over to use the default browser built-in controls, it uses "disabled" instead of "hidden".

@SemihGk Thank you for bringing this to our attention. I will get a fix put together today.

[SemihGk]

Thank you, @vaage. We look forward to waiting the fix then.