RE: TTML2 comments on roll-up and paint-on captions

@GlennG - Although certainly a desirable thing for TTML to handle for the application of conversion from 608/708, it is unclear that it is possible.  The main reason is that the timing models are so radically different.  TTML is explicit on both begin and end.  608/708 are both implicit on both timings.  The 608/708 timing is entirely dependent on its placement in the video.  Painton is accomplished by virtue of the text becoming incrementally available over time.

Timing on <spans> is generally less overhead than implementing 608 midrow codes (color, etc) on <span>.

Offhand I don't see any way to facilitate conversion of 608/708 painton in TTML without explicitly providing the timing of the "chunks" which necessarily requires that the timing be on <span>.

Smooth scroll is purely a decoder function. 608/708 have no such decoder control by the author, so adding such an authorial control would be new (which is fine to propose, but unrelated to 608/708). FYI, smooth scrolling can be accomplished by a presentation engine as described in: https://css-tricks.com/snippets/jquery/smooth-scrolling/

Those interested in comparing the CTA 608/708 DTVCC test bitstreams with the equivalent hand-coded IMSC1 text are welcome to join CTA R4.3WG1.

Regards,

               Mike

From: Nigel Megitt [mailto:nigel.megitt@bbc.co.uk]
Sent: Thursday, July 13, 2017 4:23 AM
To: Goldstein, Glenn <glenn.goldstein@viacom.com>; public-tt@w3.org
Subject: Re: TTML2 comments on roll-up and paint-on captions

> This approach would simplify the conversion of 608/708 captions to TTML, and eliminate the complexity and clutter of overlapping cues and timed <span> tags.

Please could you explain more about the impact of the "complexity and clutter" for you?

Kind regards,

Nigel


From: "Goldstein, Glenn" <glenn.goldstein@viacom.com<mailto:glenn.goldstein@viacom.com>>
Date: Wednesday, 12 July 2017 at 23:17
To: "public-tt@w3.org<mailto:public-tt@w3.org>" <public-tt@w3.org<mailto:public-tt@w3.org>>
Subject: TTML2 comments on roll-up and paint-on captions
Resent-From: <public-tt@w3.org<mailto:public-tt@w3.org>>
Resent-Date: Wednesday, 12 July 2017 at 23:18

In my opinion, the approach taken for supporting roll-up and paint-on modes (2 important caption styles in the US) could be simplified by having explicit regions attributes, as in tts:paintmode="rollup" or tts:paintmode="painton". For rollups, the scrolling style could also be designated as "smooth" or "discrete".

This approach would simplify the conversion of 608/708 captions to TTML, and eliminate the complexity and clutter of overlapping cues and timed <span> tags.


Glenn Goldstein
SVP, Chief Technology Convergence Officer
Viacom MTS