[whatwg] HTML5 video: frame accuracy / SMPTE

Silvia Pfeiffer silviapfeiffer1 at gmail.com
Fri Jan 21 13:49:20 PST 2011

On Sat, Jan 22, 2011 at 8:04 AM, Philip Jägenstedt <philipj at opera.com> wrote:
> On Fri, 21 Jan 2011 20:11:30 +0100, Gregory Maxwell <gmaxwell at gmail.com>
> wrote:
>> On Fri, Jan 21, 2011 at 1:38 PM, Rob Coenen <coenen.rob at gmail.com> wrote:
>>> I still want the API to support seeks to exact frames.
>>> eg when I build some GUI that allows the user to click on a button that
>>> says
>>> "explosion shot 1 at 00:31:02.15" then I want the player to seek to
>>> 00:31:02.15 exactly and not to say, 00:31:02.01 simply b/c that's where a
>>> keyframe happens to be.
>> It's unthinkable to me that it wouldn't at least offer exact seeking
>> as an option. There are too many interesting programmatic things that
>> you can't do without exact seeking.  Though I don't think that has
>> anything to do with the default behavior. Since the default behavior
>> is already inconsistent perhaps it should just be formally declared to
>> be at the implementers whim.
> Since, as you say, the behavior is currently inconsistent, there is still
> time to agree on something that makes sense and have everyone implement
> that. I think the best default is keyframe seeking and haven't seen any
> strong arguments for accurate seeking as the default yet.
> Concretely: Add seek(time, flags) where flags defaults to nothing. Accurate
> seeking would be done via seek(time, "accurate") or some such. Setting
> currentTime is left as is and doesn't set any flags.

I would expect that a Web developer that uses seek without a flag
would expect exact timing (as exact as your audio samples are). So, I
would make that the default. But I would also introduce
"snap_to_frame" and "snap_to_keyframe" as options on seek, so that you
can get to the start time of the frame that your timing is on or you
can get to the previous keyframe. I think from a Web developer POV
that makes the most sense.


> Most of the plumbing is already in the spec:
> http://whatwg.org/html#dom-media-seek
> --
> Philip Jägenstedt
> Core Developer
> Opera Software

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