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

Mark Callow callow_mark at hicorp.co.jp
Tue Jul 17 21:04:16 PDT 2012

On 18/07/2012 00:17, Silvia Pfeiffer wrote:
> I think this is simply an idea that hasn't been raised before. I like
> it. Though even then sometimes there may be nothing when there is no
> explicit poster and preload is set to none.
The language gives me the impression that drawing nothing was a
deliberate choice, in particular because later on it says:

    When the |drawImage()
    method is passed an animated image as its image argument, the user
    agent must use the poster frame of the animation, or, if there is no
    poster frame, the first frame of the animation.

Speaking of which, how does one specify the "poster frame" for an
animated image? There is no poster attribute on an img element. Is this
something specified in the file format? A quick search didn't reveal any
such for animated GIF or APNG files.

Drawing a video's poster, when available, seems much more user-friendly
to me.



> On Tue, Jul 17, 2012 at 9:58 AM, Mark Callow <callow_mark at hicorp.co.jp> wrote:
>> The spec. for CanvasRenderingContext2D.drawImage says draw nothing when
>> a video element's readyState is  HAVE_NOTHING or HAVE_METADATA. I was
>> wondering why this was chosen vs. drawing the poster. A search in the
>> list archive didn't turn up any discussion or explanation.
>> Regards
>>     -Mark

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