Prevent non native text tracks from leaking cuechange event listeners

[gesinger]

Due to a new updateDisplay function being generated on each invocation of the textTracksChanges function within emulateTextTracks of Tech, the cuechange event listener which called updateDisplay was not getting removed when looping through text tracks. This created a leak where updateDisplay could be called many times on a single track cuechange event.

An example of this can be seen by running the following:

var player = videojs('my-video', {
  html5: {
    nativeTextTracks: false
  }
});

player.on(‘ready’, function() {  
  var track = player.addTextTrack('captions');
  track.addCue(new VTTCue(1, 2, 'Test'));
  track.mode = 'showing';
  track.mode = 'showing';
  track.mode = 'showing';
  player.tech_.on('texttrackchange', function() { console.log('Text track change'); });
  player.play();
});

When a cuechange is reached (the first being at 1 second), texttrackchange will be triggered 3 times (one for each set of track.mode).

This change moves the updateDisplay function outside of the textTracksChanges function, so that it will not be regenerated on each call of textTracksChanges.

[pam]

Tests passed. Automated cross-browser testing via Sauce Labs and Travis CI shows that the JavaScript changes in this pull request are: CONFIRMED

Commit: 32a4b8dcd649be2b9e6448d835f76511a9d6cbf3
Build details: https://travis-ci.org/pam/video.js/builds/92882743

(Please note that this is a fully automated comment.)

[gkatsev]

no need to bind the error function (not that you technically can do that).

[gesinger]

Nice catch. Thanks!

[pam]

Tests passed. Automated cross-browser testing via Sauce Labs and Travis CI shows that the JavaScript changes in this pull request are: CONFIRMED

Commit: 24d7953
Build details: https://travis-ci.org/pam/video.js/builds/93072923

(Please note that this is a fully automated comment.)

[gkatsev]

LGTM

[mmcc]

LGTM