[whatwg] HTML5 video: frame accuracy / SMPTE

Eric Carlson eric.carlson at apple.com
Wed Jan 12 05:32:58 PST 2011

On Jan 12, 2011, at 12:42 AM, Philip Jägenstedt 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 Jägenstedt <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.


[1] http://developer.apple.com/library/ios/#documentation/AVFoundation/Reference/AVPlayer_Class/Reference/Reference.html%23//apple_ref/occ/instm/AVPlayer/seekToTime:toleranceBefore:toleranceAfter:

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