HLS playback treats ISMC1 subtitles as VTT if URLS doesn't have extensions.

[duggaraju]

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

What version of Shaka Player are you using?
3.3.2

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?
Both

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

What browser and OS are you using?
Chrome/Edge Windows 11

For embedded devices (smart TVs, etc.), what model and firmware version are you using?

What are the manifest and license server URIs?
https://lldemo-usw22.streaming.media.azure.net/bc26fae2-d0d5-45f7-931e-5de6f8588127/07e87ae7-02af-44ae-a8f2-c2997c397342.ism/manifest(format=m3u8-cmaf).m3u8

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

What did you do?

Just play the URL and see if subtitles work.

What did you expect to happen?
subtitles work as expected.

What actually happened?

The issue lies with this code in hls_parser.js

async createStreamInfoFromMediaTag_(tag) {
goog.asserts.assert(tag.name == 'EXT-X-MEDIA',
'Should only be called on media tags!');
const groupId = tag.getRequiredAttrValue('GROUP-ID');
let codecs = '';
/** @type {string} */
const type = this.getType_(tag);
// Text does not require a codec.
if (type != shaka.util.ManifestParserUtils.ContentType.TEXT && groupId &&
this.groupIdToCodecsMap_.has(groupId)) {
codecs = this.groupIdToCodecsMap_.get(groupId);
}

It explicitly ignores the codec for text streams and then later the code assumes subtiltes to be VTT if codec is not present:

async guessMimeType_(contentType, codecs, playlist, variables) {
const HlsParser = shaka.hls.HlsParser;
const ContentType = shaka.util.ManifestParserUtils.ContentType;
const requestType = shaka.net.NetworkingEngine.RequestType.SEGMENT;

goog.asserts.assert(playlist.segments.length,
    'Playlist should have segments!');
const firstSegmentUri = this.variableSubstitution_(
    playlist.segments[0].absoluteUri, variables);

const parsedUri = new goog.Uri(firstSegmentUri);
const extension = parsedUri.getPath().split('.').pop();
const map = HlsParser.EXTENSION_MAP_BY_CONTENT_TYPE_[contentType];

const mimeType = map[extension];
if (mimeType) {
  return mimeType;
}

if (contentType == ContentType.TEXT) {
  // The extension map didn't work.
  if (!codecs || codecs == 'vtt' || codecs == 'wvtt') {
    // If codecs is 'vtt', it's WebVTT.
    // If there was no codecs string, assume HLS text streams are WebVTT.
    return 'text/vtt';
  } else {
    // Otherwise, assume MP4-embedded text, since text-based formats tend
    // not to have a codecs string at all.
    return 'application/mp4';
  }
}

This is because our URLs do not have an extension and it doesn't seem to do a HEAD request for subtitles so instead guesses the mime type incorrectly.