[whatwg] HTML5 video seeking

Aaron Colwell acolwell at chromium.org
Tue Nov 15 10:19:34 PST 2011

Hi Philip,

Thanks for the link. It took me a little while to read the whole thread.

I'm not looking to support multiple styles of seeking. I was just noticing
that the spec text does not appear to allow you to seek to a position
different from the exact time specified. Steps 5-7 appear to bound the "new
playback position" based on the start, end, and seekable ranges, but I'm
not seeing any text that allows "new playback position" to be modified
based on other factors like keyframes locations. I'm just trying to
determine if we are intentionally requiring frame accurate seeking at this
point or am I just misinterpreting some part of the spec.


On Tue, Nov 15, 2011 at 1:30 AM, Philip Jägenstedt <philipj at opera.com>wrote:

> On Tue, 15 Nov 2011 00:49:32 +0100, Aaron Colwell <acolwell at chromium.org>
> wrote:
>  Hi,
>> I was looking at the seeking
>> algorithm<http://www.whatwg.**org/specs/web-apps/current-**
>> work/multipage/the-video-**element.html#seeking<http://www.whatwg.org/specs/web-apps/current-work/multipage/the-video-element.html#seeking>
>> >
>> and
>> had a question about step 10.
>> 10. Wait until the user agent has established whether or not the media
>> data for the new playback position is available, and, if it is, until it
>> has decoded enough data to play back that position.
>> Does this mean the user agent must resume playback at the exact location
>> specified?
>> What if the nearest keyframe is several seconds away?
>> Is the UA expected to decode and toss the frames instead of starting
>> playback at the nearest keyframe?
>> On desktop machines I don't think this would be a problem, but on mobile
>> devices it might be since the hardware may not be able to decode
>> significantly faster than realtime. What is the intended behavior for such
>> constrained devices?
>> Aaron
> This was last discussed in the huge thread "HTML5 video: frame accuracy /
> SMPTE" where I made the suggestions [1] to introduce a seek() function to
> allow both frame-accurate and fast seeking. If you like that idea maybe we
> can just spec and implement it?
> [1] http://lists.whatwg.org/htdig.**cgi/whatwg-whatwg.org/2011-**
> January/029806.html<http://lists.whatwg.org/htdig.cgi/whatwg-whatwg.org/2011-January/029806.html>
> --
> Philip Jägenstedt
> Core Developer
> Opera Software

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