fix(toM3u8): set label for vttPlaylist from label instead of lang

[RomeroDiver]

Fix the issue when the subtitles' label property was set from lang instead of label

[codecov]

Codecov Report

Merging #161 (419aee1) into main (cd75be1) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #161   +/-   ##
=======================================
  Coverage   94.34%   94.34%           
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  Files          19       19           
  Lines         778      778           
  Branches      242      242           
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  Hits          734      734           
  Misses         44       44           

Impacted Files	Coverage Δ
src/toM3u8.js	98.75% <100.00%> (ø)

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[gkatsev]

I believe this isn't the spec-compliant way of labeling text tracks. The expected way is with a Label element.
Also see answer here #153 (comment)

there's some direction on how to do it with a label element here videojs/video.js#6960 (comment)

[RomeroDiver]

I agree with your comment, however this fix is exactly to make the Label element work. E.g. without the fix the following is not working properly - the Label element is not read,

<AdaptationSet mimeType="text/vtt" lang="en">
      <Role schemeIdUri="urn:mpeg:dash:role" value="subtitle"/>
      <Label>English</Label>
      <Representation id="12" bandwidth="256">
        <BaseURL>url</BaseURL>
      </Representation>
    </AdaptationSet>

[RomeroDiver]

What do you think? I think this change is according to the specs

[gkatsev]

Sorry, haven't had a chance to test it yet.

[gkatsev]

Finally got around to this. Confirmed that this does what's expected.

I also found a test source with a labeled text track https://demo.unified-streaming.com/k8s/features/stable/video/tears-of-steel/tears-of-steel-hoh-subs.ism/.mpd (though, VHS won't be able to play it, since VHS doesn't support IMSC currently).