[whatwg] HTML5 video: frame accuracy / SMPTE

Gregory Maxwell gmaxwell at gmail.com
Fri Jan 21 14:19:56 PST 2011

On Fri, Jan 21, 2011 at 5:11 PM, Glenn Maynard <glenn at zewt.org> wrote:
> Should there be any consistency requirements for fast seeking?
> This could have unexpected side-effects.  Should this be allowed?  I'd
> suggest that fast seeking should always be consistent with itself, at
> least for a particular video instance.

Good point.

> On Fri, Jan 21, 2011 at 5:05 PM, Gregory Maxwell <gmaxwell at gmail.com> wrote:
>> One question about inexact seeking is what should the client do when
>> the current playtime is closer to the requested time than what the
>> inexact seek would provide?
> The above would also answer your question: seeking would be unaffected
> by the current play cursor.

It would, but it also results in some pretty perplexing and unfriendly
behavior... where the user hits the 5-seconds forward button and ends
up going 4-seconds backwards, only to press the button again and
repeatedly land on the same spot.

It would be possible to require that the derivative with respect to
the current play time have the same sign as the request to avoid this
perplexing behavior (and this appears to be what standalone media
players appear to do with forward and backward buttons) but it runs
into the consistency problems you've raised.

So I'm seeing three relevant dimensions: Consistency, Accuracy of the
position, and Accuracy of the direction.  Consistency and accuracy of
the direction are not compatible unless the seeking is exact.

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