863488 - [webvtt] captions do not display unless play() is called

Status: RESOLVED WORKSFORME

(Core :: Audio/Video: Playback, defect)

Description

[Ralph Giles (:rillian)]

If we add a track element to a video element and then call video.currentTime=foo, the playback time changes and the video updates to show the requested frame, but the currently active caption does not display.

If one subsequently calls play() or clicks the play button on the controls the caption immediate displays.

E.g. after loading https://people.xiph.org/~giles/2013/vtt-02.html text should be visible on the video frame.

Comment 1

[Ralph Giles (:rillian)]

Tested with https://github.com/RickEyre/mozilla-central.git integration branch commit de894e21b1ae69c07648e917f3ccd5052a84e73b and media.webvtt.enabled=true in about:config.

Comment 2

[Ralph Giles (:rillian)]

FWIW, Chrome Canary 28 doesn't show the caption on initial page load or shift-reload, but does on a simple reload.

Comment 3

[Rick Eyre (:reyre)]

What's our stance on this Ralph? Do we just want parity with Chrome, or should we implement the behaviour you suggested?

Comment 4

[Rick Eyre (:reyre)]

See previous comment. Forgot to needinfo.

Comment 5

[Rick Eyre (:reyre)]

See comment 3.

Comment 6

[Ralph Giles (:rillian)]

I think we should implement the behaviour I suggested.

With today's nightly 31.0a1 (2014-04-07) the behaviour is improved. If I just visit the example page from the URL field subtitles render. If I reload the page with 'ctrl-R' sometimes it displays and sometimes it doesn't. Looks like we have a race?

Comment 7

[Rick Eyre (:reyre)]

The race is probably because 'onloadedmetadata' hasn't been changed to fire after the tracks have loaded yet. See bug 882669 for details. I'll probably be tackling that bug next and it's dependent bugs so this should be solved once that lands.

Comment 8

[Ada [:adalucinet]]

With the following STR:
1. Load http://people.mozilla.org/~rgiles/2013/demo.html and play.
2. Pause when the subtitle is displayed.
3. Enter fullscreen.
Actual result: the subtitle is not displayed in fullscreen mode unless Play is clicked again. 
Reproducible with Firefox 31 beta 8, latest Nightly and latest Aurora on Windows 7 x64 and Mac OS X 10.9.4.

Is the above issue related to this bug?

Comment 9

[Rick Eyre (:reyre)]

Yes, that issue sounds like it's related to this bug. I'll see if I can look into it eventually.

Comment 10

[Benjamin Chen [:bechen]]

The bug had been fixed by other bugs.