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Video subtitles delay
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Description

The subtitles are shown with a delay with the HTML5 player.
Here's an example of a video with synchronized subtitles shown too late when played with the HTML5 player:
https://commons.wikimedia.org/wiki/File:Around_the_Corner_%281937%29_24fps_selection.webm

Some subtitles are shown at the right time, but most have a delay.
It seems at least partially caused by the subtitles fading animation.

Event Timeline

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Restricted Application added a subscriber: Aklapper. · View Herald TranscriptApr 19 2015, 10:59 AM

Hmm, did you check the time marks in the subtitles file to make sure this is actually a software issue and not simply how the time marks were set?

Some subtitles are shown at the right time, but most have a delay.

Same experience here in FF37, but delay is always small (under one second). And I don't get any fading animation here....

Does this also happen with other videos, or just with this one?

Aklapper changed the task status from Open to Stalled.Apr 23 2015, 10:10 AM
TheDJ added a subscriber: TheDJ.Aug 7 2015, 8:37 PM

The subtitles are only added AFTER the last timeupdate event passed the time in which the subtitle needs to be presented and then removes and reads the subtitle multiple times per second during it's presentation. It also does multiple expensive DOM lookups in that loop.

So it's not too surprising that it's a bit late...
Let's hope we soon have VideoJS

Restricted Application added a subscriber: Matanya. · View Herald TranscriptAug 7 2015, 8:37 PM
Jdforrester-WMF triaged this task as Low priority.Sep 4 2015, 6:56 PM
Jdforrester-WMF moved this task from Untriaged to Backlog on the Multimedia board.Sep 4 2015, 7:02 PM

Hmm, did you check the time marks in the subtitles file to make sure this is actually a software issue and not simply how the time marks were set?

Yes, if you download the video and the subtitles, you can see that there's no delay.

Some subtitles are shown at the right time, but most have a delay.

Same experience here in FF37, but delay is always small (under one second). And I don't get any fading animation here....

The more I check it, the more I think it has to do with the appearing and fading animations when showing and hiding subtitles. That kind of animation isn't found on regular subtitles, so it could be removed.
Or alternatively, the subtitles could be shown sooner to make up for that delay. And the animation would have to be removed anyway when a new subtitle has to be shown before the appearing and fading animations can be accomplished.

Aklapper changed the task status from Stalled to Open.Nov 18 2016, 4:07 PM
brion moved this task from Backlog to Player-Old on the TimedMediaHandler board.Apr 23 2018, 11:03 PM