Is bopomofo needed for on-screen captions?

[r12a]

The question arose for TTML2. See w3c/ttml2#253

It is being argued that

If Chinese subtitlers do not use bopomofo currently, are not asking for bopomofo support in the near future, and no one will be able to prove implementation support of bopomofo, is this really something that needs to be solved in TTML2?

If you have a view on this or have an insight into use of bopomofo for subtitling, you may want to contribute to that issue thread.

[dae-kim]

It will be extremely helpful if we can reference current subtitle examples of bopomofo and how they markup bopomofo -- is there a published CSS module or other document detailing the semantics?

[bobbytung]

Only a few samples for preschool education:
https://www.youtube.com/watch?v=yiQKOD4sE84

In this case, ruby position: inter-charactoer should be considered as a part of the spec.
https://www.w3.org/TR/css-ruby-1/#inter-character-layout

But I'm still working on how to let tone marks (that is ˋˇˊ) on right position, may be try Opentype feature. For TTML, I think next version?

[bobbytung]

Bopomofo layout, especially tone marks' position need more work with font technology.