[whatwg] HTML5 video: frame accuracy / SMPTE

Gregory Maxwell gmaxwell at gmail.com
Fri Jan 21 13:15:43 PST 2011

On Fri, Jan 21, 2011 at 4:04 PM, Philip Jägenstedt <philipj at opera.com> wrote:
> 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.
> Most of the plumbing is already in the spec:
> http://whatwg.org/html#dom-media-seek

I don't like "keyframe seeking" as the default. "Keyframe seeking"
assumes things about the container, codec, and encoding which may not
be constants or even applicable to all formats. For example a file
with rolling intra may have no keyframes,  and yet are perfectly
seekable.  Or if for some reason a client can do exact seeking very
cheaply for the request (e.g. seeking to the frame immediately after a
keyframe) then that ought to be permitted too.

I'd rather say that the default should be an implementation defined
accuracy, which may happen to be exact, may differ depending on the
input or user preferences, etc.

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