When the following properties have changed for an active cue, the rules for updating the text track rendering should be run:

the properties corresponding to the 'font' shorthand, including 'line-height'
'white-space'

When an active cue gets one of the following properties changed, the rules for updating the text track rendering should be run:
vertical
snapToLines
line
position
size
align
text

Also when changing startTime and endTime we might want to check if the cue should be currently active or not.

This should be done even if the video is paused, except if video playback hasn't ever started yet.

Also when the native controls become visible or not visible.

This bug was cloned to create bug 18184 as part of operation convergence.

Not sure I agree about doing it when the controls appear/disappear, but I guess we should at least allow it.

Turns out the spec already does it for when the controls appear/disappear.

Still need to do startTime/endTime changes. Actually, it's more than that, because it looks like we don't yet handle showing captions when they're added while the video is paused, either.

(Not quite sure how to fix that.)

Checked in as WHATWG revision r7430.
Check-in comment: Updating cues' styles and properties dynamically should be visible immediately
http://html5.org/tools/web-apps-tracker?from=7429&to=7430

I'm not 100% sure this fix (see diff in next comment) really works, so if you see a problem with it please don't hesitate to reopen this bug (or file a new one).

Checked in as WHATWG revision r7835.
Check-in comment: Make adding a cue, or changing its timings, work when the video is paused.
http://html5.org/tools/web-apps-tracker?from=7834&to=7835

I think you overlooked this part in the two commits above:

"This should be done even if the video is paused, except if video playback hasn't ever started yet."

Otherwise it looks good I think.

I also think that this line was changed by error:

-<!-- EDITOR NOTES  -*- mode: Text; fill-column: 100 -*-
+ne<!-- EDITOR NOTES  -*- mode: Text; fill-column: 100 -*-

zcorpan: What's the right way to trigger this when paused-but-not-started? Just call "time marches on" in the paragraph that adds the stuff to "list of newly introduced cues" when the element is paused, unless its "show poster flag" set is set?

Yeah... or maybe bail out of "time marches on" as the first step if "show poster flag" is set.

Checked in as WHATWG revision r7965.
Check-in comment: Make cues that are added while a video is paused get rendered before it gets unpaused.
http://html5.org/tools/web-apps-tracker?from=7964&to=7965

Don't the cases that invoke "time marches on" in http://html5.org/tools/web-apps-tracker?from=7834&to=7835 (except the first one) also need to check the show poster flag? Does the new commit add anything that wasn't already required?

In answering your questions, I concluded that this was a big mess, and I tried fixing this all over again. Take a look at the next text, let me know what you think. Thanks!

http://html5.org/r/7990

+      false, <span>queue a task</span> to <span>fire a simple event</span> named <code
+      title="event-media-play">play</code> at the element, <span>queue a task</span> to <span>fire a
+      simple event</span> named <code title="event-media-playing">playing</code> at the element, and
+      then, if the element's <span>show poster flag</span> to false, first set it to false and then
+      run the <i>time marches on</i> steps.</p>

"then" being after the tasks have been queued? Or after they have run? If the latter, maybe it would be clearer to queue a third task?

Also s/to false/is true/

Otherwise it looks good, I think.

I meant it to happen synchronously, before the tasks run, after they're queued. Normally I'd queue them last, but then it's unclear if the queuing depends on the flag or not, etc. Anyway I made this better by using a list instead of a single paragraph.

Thanks for reviewing it!

Checked in as WHATWG revision r8012.
Check-in comment: Clarify how autoplay and subtitles interact. Mostly editorial cleanup, though I change a 'false' to a 'true', so not entirely.
http://html5.org/tools/web-apps-tracker?from=8011&to=8012