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Re: [media-and-entertainment] Frame accurate seeking of HTML5 MediaElement

From: Nigel Megitt via GitHub <sysbot+gh@w3.org>
Date: Wed, 13 Jun 2018 10:37:04 +0000
To: public-web-and-tv@w3.org
Message-ID: <issue_comment.created-396893004-1528886223-sysbot+gh@w3.org>
> how the imsc.js library handles this

@jpiesing I can't speak for @palemieux obviously but my understanding is that imsc.js does not play back video and therefore does not do any alignment; it merely identifies the times at which the presentation should change. 

However it _is_ integrated into the [dash.js](https://github.com/Dash-Industry-Forum/dash.js/) player which does need to synchronise the subtitle presentation with the media. I believe it uses Text Track Cues, and from what I've seen they can be up to 250ms late depending on when the _Time Marches On_ algorithm happens to be run, which can be as infrequent as every 250ms, and in my experience often is.

As @Daiz points out, that's not nearly accurate enough.

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