[whatwg] HTML5 video: frame accuracy / SMPTE

Chris Pearce chris at pearce.org.nz
Tue Jan 11 15:00:55 PST 2011

On 12/01/2011 11:20 a.m., Rob Coenen wrote:
> I can imagine there are 'virtual' frames, where say frame 1 to 10 is
> actually the same frame and internally encoded as frame 1 with a duration of
> 10 frames?

Yes, as I understand it, this is a legal encoding.

> Even then I'd like the 'virtual' FPS of the WebM file exposed to the
> webbrowser- similar to how my other utilities report a FPS.

If the 'virtual' FPS value isn't provided by the container, and given 
that the frame durations could potentially have any distribution and 
that the media may not be fully downloaded, how can this be effectively 

> This way one could build web-tools in HTML5 that allow to access each
> individual frame and do other things than simply playing back the movie in a
> linear fashion from beginning to end.

I we've discussed this sort of thing before, and roughly agreed that 
we'd look at processing frame data in a per-frame callback which runs in 
a web worker thread, if we could agree on some use cases which couldn't 
be achieved using SVG filters.

That discussion was in this thread:

Chris P.

> -Rob
> On Tue, Jan 11, 2011 at 10:05 PM, Chris Pearce<chris at pearce.org.nz>  wrote:
>> On 12/01/2011 10:58 a.m., Rob Coenen wrote:
>>> Intresting- I didn't know that variable frame-rate videos were actually
>>> being used for HTML5 video.
>> WebM videos have no fixed frame rate. This format is supported in Firefox
>> 4, Chrome, and Opera.
>> Chris P.

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