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[Bug 13060] New: Consider MJPG files like <video> when used as the image argument for drawImage()

From: <bugzilla@jessica.w3.org>
Date: Sat, 25 Jun 2011 16:38:47 +0000
To: public-html@w3.org
Message-ID: <bug-13060-2495@http.www.w3.org/Bugs/Public/>
http://www.w3.org/Bugs/Public/show_bug.cgi?id=13060

           Summary: Consider MJPG files like <video> when used as the
                    image argument for drawImage()
           Product: HTML WG
           Version: unspecified
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: HTML Canvas 2D Context (editor: Ian Hickson)
        AssignedTo: ian@hixie.ch
        ReportedBy: david.humphrey@senecac.on.ca
         QAContact: public-html-bugzilla@w3.org
                CC: mike@w3.org, public-html-wg-issue-tracking@w3.org,
                    public-html@w3.org


Created attachment 1005
  --> http://www.w3.org/Bugs/Public/attachment.cgi?id=1005
DrawImage test case with MJPG (traffic web cam)

Currently, the canvas2d drawImage() spec 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."

It then goes on to discuss the special case of HTMLVideoElements:

"When the image argument is an HTMLVideoElement, then the frame at the current
playback position must be used as the source image, and the source image's
dimensions must be the intrinsic width and intrinsic height of the media
resource (i.e. after any aspect-ratio correction has been applied)."

I'd like to suggest that MJPG files are often used in place of video,
especially with security cameras and other web camera feeds.  Some browser
vendors already take the same position, for example Chrome and Safari, which
will use the current image (frame) of the MJPG when it is passed to
drawImage().  Firefox currently tries to do what the spec says, and load the
first frame.  I've filed a bug with Mozilla, as well:

https://bugzilla.mozilla.org/show_bug.cgi?id=667206

I believe that WebKit's behaviour is useful and least surprising here, even
though not spec compliant.  I'd like to suggest that this behaviour be
considered as the correct one for the spec going forward, and that spec be
changed.

I've included a simple test case.

Thanks for considering this.

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Received on Saturday, 25 June 2011 16:38:53 UTC

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