Uncaught TypeErrors when switching subtitle tracks

[fredrik-telia]

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

What version of Shaka Player are you using?
Latest (main)

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

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

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

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

What browser and OS are you using?
Chrome, macOS

What are the manifest and license server URIs?

What configuration are you using? What is the output of player.getConfiguration()?

What did you do?
Playing HLS stream with two subtitle tracks, switching tracks causes uncaught TypeError

What did you expect to happen?
No errors

What actually happened?
Could it be that there's a typo in hls_parser.js

shaka-player/lib/hls/hls_parser.js

Line 3370 in 7fa40fd

'webvtt': 'txt/vtt',

?

Changing this to text/vtt makes the TypeErrors go away

[martinstark]

There seems to be a deeper issue in hls_parser.js that causes one track to be assigned text/vtt and the second track to be assigned txt/vtt when guessing mimetypes, despite both having the same file extension.

I haven't debugged it fully, the PR provided by Fredrik fixes the issue by correcting the bad mime type, but it's confusing me why shaka would choose two different ones for near identical tracks.

[joeyparrish]

it's confusing me why shaka would choose two different ones for near identical tracks.

We don't know the extension until we load the playlist, and since v4.3.0, we only load the playlists of tracks that we are streaming.

One instance was hard-coded, and the other used a lookup table that contained a typo. Sorry for the trouble, and thanks for the fix!

[martinstark]

Workaround while waiting for a new shaka release:

  shaka.text.TextEngine.registerParser(
    "txt/vtt",
    () => new shaka.text.VttTextParser()
  );