[whatwg] Why does CanvasRenderingContext2D.drawImage not draw a video's poster?

Charles Pritchard chuck at jumis.com
Wed Jul 25 20:58:53 PDT 2012

On Jul 21, 2012, at 1:20 PM, Silvia Pfeiffer <silviapfeiffer1 at gmail.com> wrote:

>> I'm not opposed to the idea, but I'm failing to see the benefit.
> The advantage clearly is that if you have a canvas that is copying
> data out of the video, it includes the poster without having to write
> custom code for it. The poster is an integral part of the video (it's
> not distinguishable by the user whether it is a separate picture or a
> frame from the video), so I don't see why it should need custom
> handling.

Canvas is a lot of low level custom code. As a polyfill, it seems that Canvas coders ought to consider checking for a poster attribute in their code path regardless of how this goes.

>> Still, if
>> there's going to be one, we're going to need an onposterloaded event.
> Why? onmetadataloaded provides a sufficiently stable stuation: either
> the poster img or video frame is then loaded (if @preload is not
> "none") or it's black (if @poster is not set and @preload is "none").

Seems like a good place to spec this. +1.

I'm not up to speed on the video spec, but if this behavior for poster is not in there, consider proposing it to the editor(s).


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