[webkit-help] Get the output of WebKit as a RGBA image... Is this possible?

Efren CD efrencd at gmail.com
Sat Oct 23 10:47:16 PDT 2010

I am trying to code a tiny application which is able to output the contents
redenred by a HTML/Javascript layout engine to the output of a secondary
graphic card. The card is a profesional video capturer/renderer which has
its own SDK an it is able to KEY  "alpha channeled" (RGBa) contents over
live video signal using an internal key functionality.

I need to get the contents rendered by the layout engine in RGBa format
(with alpha channel information) so that its contents could be properly
keyed using the internal Key function of the Decklink Card.

The layout engine should make use of all its functionality like Javascript,
PlugIns Support (Flash/Silverlight, etc.) and Audio Out to the Decklink

Here there is a sample page which its contents shoud be keyed:


The idea is to input a live video to the decklink card and then the app
overlays the sample.html page over the video using the internal key
functionality of the Decklink card.

Is that Possible?

PD: I've been talking about this issue in the Decklink Developers mailing
list and here you have an interesting comment that can help you get a
understanding of this issue:

"Taking a 32bit PNG should be no problem, the Decklink API allows you to
create a 32bit ARGB data block using IDeckLinkOutput.CreateVideoFrame()
"bmdFormat8BitARGB" as the "pixelFormat" property, and the card will key
over your input video using the Alpha as the base key, and then you can ramp
up and down overall Key Level of the graphic using IDeckLinkKeyer.SetLevel.

Where I think you'll have a problem is any browser will composite your HTML
, PNG, Flash, Silverlight against an opaque document background, at which
point I'm
not sure how you get hold of the combined Alpha channel you need to fill
your ARGB frame data buffer. You could certainly scrape the browsers client
window as a 24 bit colour bitmap, and I suppose you could use a single
colour to indicate where to set the Alpha to 0x00 to let the video through,
but that won't help you
much for partial transparency."

Thanks in advance.
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