Text Management refactoring

[jeremco]

Hi

This pull request contains some refactoring to have a better comprehension on how subtitles and captions are working on dash.js.
One new text controller is added to manage tracks. The way source buffer controller is created is hidden by a text buffer controller proxy. The text source buffer is dedicated to manage and create cues.
The code relative to text is then centralized and is more easy to understand. Each 'class' has now its own responsability

Jérémie

[dsparacio]

Not sure what this is solving? I get that the code may not be ideal but this CR creates a ton of code climates alerts. Have you tested this with ALL types of captions. Embedded 608/708 fragmented ISo encaplustaed, VTT and TTML Sidecar?

[TobbeEdgeware]

At first glance, this looks good. I'll try to go through this in the next few days to understand how it works and check if our various subtitle samples are still working properly.

[jeremco]

@AkamaiDASH : The idea is to centralized treatments for text, because in actual code, there is some specifics text treatments made in MediaPlayer, in BufferController and so on
If the treatment is centralized, it will help to find any problems about text.
The idea is although to have only one 'responsibility' for classes. Because, here we have a text source buffer that :

• Manage track selection
• Display HTML for embedded captions
• And fills browser text track queue.
  It results in a big file, that is not very comprehensive at first glance.

I have test on all text streams of the dash-if sample page.

[dsparacio]

We are testing with this PR a bit but should make it into the release. Looks good at high level.

[dsparacio]

@jeremco Thanks for the details and thanks for the commit. Looks nice.

[TobbeEdgeware]

I checked the various subtitle samples included in the reference player content list.
I found a bug when switching between content that I tracked down to the resetEmbedded function in TextSourceBuffer. Since the textTracks is set to null in the abort() function, we must have a test in the resetEmbedded function.

function resetEmbedded() {
    eventBus.off(Events.VIDEO_CHUNK_RECEIVED, onVideoChunkReceived, this);
    if (textTracks !== null) {
        textTracks.deleteAllTextTracks();
    }

I made a PR to this PR for this.

After the fix, all subtitles work. There is still an issue with the mixed Subtitle embedded-captioning sample where the subtitles is strangely formatted in the reference player, but that is nothing new.

I'll look around a bit more, but in general, I think this looks good for inclusion in the release.

[jeremco]

Thanks for the PR. I have accepted your modification