[whatwg] HTML5 video: frame accuracy / SMPTE
philipj at opera.com
Fri Jan 21 13:40:28 PST 2011
On Fri, 21 Jan 2011 22:15:43 +0100, Gregory Maxwell <gmaxwell at gmail.com>
> On Fri, Jan 21, 2011 at 4:04 PM, Philip Jägenstedt <philipj at opera.com>
>> Since, as you say, the behavior is currently inconsistent, there is
>> 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.
>> 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:
> 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'm fine with any terminology, as long as it allows implementations to
seek to some other time than currentTime if it's (much) faster to do so.
GStreamer has the flags GST_SEEK_FLAG_ACCURATE and GST_SEEK_FLAG_KEY_UNIT,
if that's any inspiration.
> 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.
Since it will then be seen as an quality of implementation issue and there
will be no way for scripts to chose which behavior they want, then we'll
still have to do slow (accurate) seeking and nothing else.
Anyway, if all we disagree on is the default flags, then that's still
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