Features
#4089 Add parsing and rendering of WebVTT subtitles in dash.js, not relying on native texttracks events anymore. This is required for platforms like HbbTV that do not provide native WebVTT support. An example can be found here: https://reference.dashif.org/dash.js/nightly/samples/captioning/vttjs.html @dsilhavy
Improvements
#4088 Fix redundant segment download when seeking back into already buffered area @dsilhavy
#4093 In case of gaps: Check for a valid segment request using the period duration @dsilhavy
Bugfixes
#4087 Do not trigger live delay calculation multiple times at playback start @dsilhavy
#4091 If seek is called with a negative value rewrite to 0 @dsilhavy
#4092 Account for invalid starttimes provided to attachSource() @dsilhavy
#4096 Fix linting errors @dsilhavy