Full ASS support

[zoriya]

Have you read the FAQ and checked for duplicate open issues?
Yes

Is your feature request related to a problem? Please describe.

The current ASS subtitles support extract texts but does not respect the styling at 100%. We can't create a plugin to handle this since subtitles are all treated in two steps (first extract to Shaka's internal cue and then display via a renderer).

Describe the solution you'd like

It would be great to display ASS subtitle with all their styles, using libass directly. This can be done using https://github.com/ThaUnknown/jassub for example.

Since it's an external library and for a niche case, I'd understand not including this by default, but It would be nice to have a plugin for that. I'm willing to write such a plugin, but I think I'm mission some tools to do so (namely hijack the text parsing->render pipeline).

Describe alternatives you've considered

Not using Shaka for ass subtitles and make edge cases on our code. This can be fine if this is too difficult to implement.

Are you planning send a PR to add it?

I'm planning to write a plugin for that, but I won't be sending PRs to add plugin APIs.

[avelad]

It is the first time that in 3 years someone has been interested in ASS Text Parser!

Please send examples of the styles that are not supported or at least tell us that styles according to the SPEC (http://moodub.free.fr/video/ass-specs.doc)

Thank you!

[zoriya]

In my tests, the subtitle did not work at all (nothing showing). I tested with https://thaunknown.github.io/jassub/subtitles/FGOBD.ass

Shaka also lacks the ability to add fonts, so if the subtitle wants to use a weird font not available on the device it will fallback to a default font.

The more I talk about this, the more I realize It would be way easier to simply use jassub on top of the shaka instead of trying to combine the two. Sorry for then noise, I think we can close this.

[avelad]

I have found a error in the parser, I will create a PR to fix it. You are right about the font, I will investigate about it. On the other hand I have found a error that we show duplicate subtitles, I will also create a PR to fix it!

[avelad]

@zoriya To load a font you can use https://developer.mozilla.org/en-US/docs/Web/API/CSS_Font_Loading_API, it is not necessary for Shaka to know the fonts, you can load them on your website independently of Shaka.

[avelad]

I'm going to make a PR to support DVB fonts in DASH, so I'll take the opportunity to make a new public method called addFont and this will help you!