Fix for Opus audio in fragmented MP4

[bvibber]

The Opus box name is capitalized, but MediaSource expects a lowercase "opus" codec string, which was causing unexpected failures in Chrome and Firefox.

Now matches behavior of mux.js for audio tracks by forcing the box type to lowercase before returning it as a codec string.

Description

HLS streams with Opus audio tracks in fragmented MP4 weren't working in Chrome and Firefox due to reading the codec string as "Opus" with a capital "O", which MediaSource rejects.

Specific Changes proposed

Forcing the box name string to lowercase resolves the specific problem with Opus; all other known codec strings are lowercase. mux.js appears to use the same logic when returning codec strings, so this is not expected to be problematic.

Requirements Checklist

• [X] Feature implemented / Bug fixed
• [ ] If necessary, more likely in a feature request than a bug fix
  • [ ] Unit Tests updated or fixed
  • [ ] Docs/guides updated
  • [ ] Example created (starter template on JSBin)
• [ ] Reviewed by Two Core Contributors

[codecov[bot]]

Codecov Report

Merging #1219 (7a4844f) into main (bdd842a) will not change coverage. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1219   +/-   ##
=======================================
  Coverage   85.40%   85.40%           
=======================================
  Files          40       40           
  Lines        9963     9963           
  Branches     2308     2308           
=======================================
  Hits         8509     8509           
  Misses       1454     1454           

Impacted Files	Coverage Δ
src/media-segment-request.js	95.50% <100.00%> (ø)

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