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

From: Ingar Mæhlum Arntzen <ingar.arntzen@gmail.com>
Date: Wed, 13 Jun 2018 08:55:32 +0200
Message-ID: <CAOFBLLqMgGvRvEfE+RkOcS2uh=mRcXrqqm94CtEAxrsfDcGa0A@mail.gmail.com>
To: Jon Piesing via GitHub <sysbot+gh@w3.org>
Cc: public-web-and-tv <public-web-and-tv@w3.org>
With the timingsrc [1] library we are able to sync content changes outside
the video with errors <10ms (less than a frame).

The library achieves this by

- 1) using an interpolated clock approximating currentTime (timingobject)
- 2) synchronizing video (mediasync) relative to a timing object (errors
about 7ms)
- 3) synchronizing javascript cues (sequencer - based on setTimeout)
relative to the same timing object (errors about 1ms)

This still leaves delays from DOM changes to on-screen rendering.

In any case, this should typically be sub-framerate sync.

This assumes that currentTime is a good representation of the reality of
video presentation. If it isn't, but you know how wrong it is, you can
easily compensate.

Not sure if this is relevant to the original issue, which I understood to
be about accurate frame stepping - not sync during playback?

Ingar Arntzen

[1] https://webtiming.github.io/timingsrc/

2018-06-13 8:20 GMT+02:00 Jon Piesing via GitHub <sysbot+gh@w3.org>:

> It depends on the inputs to the custom subtitle rendering algorithm. How
>> do you determine when to render a text cue?
> Perhaps @palemieux could comment on how the imsc.js library handles this?
> --
> GitHub Notification of comment by jpiesing
> Please view or discuss this issue at https://github.com/w3c/media-a
> nd-entertainment/issues/4#issuecomment-396826633 using your GitHub account
Received on Wednesday, 13 June 2018 06:55:55 UTC

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