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[whatwg] HTML5 video: frame accuracy / SMPTE

From: Andrew Scherkus <scherkus@chromium.org>
Date: Wed, 12 Jan 2011 11:33:03 -0800
Message-ID: <AANLkTinFOWNYUqqg-Q7ykma=2YGUhR06wH7E9CwH4EiX@mail.gmail.com>
I implemented frame-accurate seeking in Chrome (mostly as an experiment) and
it does have the drawback of potentially being very slow.  Depending on the
type of video there can be a noticeable difference in seek time if you seek
to just-before-a-keyframe versus just-after-a-keyframe.

I do like the idea, however :)

Andrew

On Wed, Jan 12, 2011 at 5:32 AM, Eric Carlson <eric.carlson at apple.com>wrote:

>
> On Jan 12, 2011, at 12:42 AM, Philip J?genstedt wrote:
>
> > On Wed, 12 Jan 2011 09:16:59 +0100, Glenn Maynard <glenn at zewt.org>
> wrote:
> >
> >> On Wed, Jan 12, 2011 at 2:49 AM, Philip J?genstedt <philipj at opera.com>
> wrote:
> >>> (Also, it might be useful to be able to chose whether seeking should be
> fast
> >>> or exact, as frame-accurate seeking is hardly necessary in most normal
> >>> playback situations.)
> >>
> >> In an audio engine I worked on I had a seek hint like that, to
> >> indicate whether the priority was accuracy or speed.  It matters even
> >> more with video: when seeking with a seek bar, you may want to snap to
> >> keyframes, whereas bookmarks, "jump to chapter" features, etc. will
> >> often want to jump precisely.  A fast seek option would be
> >> particularly useful for files with infrequent keyframes.
> >>
> >
> > For the record, this is the solution I've been imagining:
> >
> > * add HTMLMediaElement.seek(t, [exact]), where exact defaults to false if
> missing
> >
> > * make setting HTMLMediaElement.currentTime be a non-exact seek, as that
> seems to be the most common case
> >
>   That is a very interesting idea!. Precise seeking in some video files can
> be quite slow, greater than a second is not unlikely on some devices. FWIW,
> the media playback framework on iOS has a seek method with parameters for
> the tolerance allowed before and after the seek time [1] to allow the
> programmer to choose.
>
> eric
>
> [1]
> http://developer.apple.com/library/ios/#documentation/AVFoundation/Reference/AVPlayer_Class/Reference/Reference.html%23//apple_ref/occ/instm/AVPlayer/seekToTime:toleranceBefore:toleranceAfter
> :
>
>
>
Received on Wednesday, 12 January 2011 11:33:03 UTC

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