Essentially I would like a generic take-a-dom-element-screenshot feature.
I would like to read the rendered image data, particularly from a youtube video, but really any embedded object for the purpose of creating a histogram.
This is currently possible with HTML5, img and video elements via canvas drawImage/getImageData. Are there any methods to get the rendered image data from embedded objects such as flash?
No, the embedded object's bitmap is isolated from the rest of the DOM and you cannot access it out-of-the-box. In reality the embedded object is just an application showing its "window" inside the client window.
If you will be able to use the object's bitmap as source depends entirely on the object itself and if it exposes the bitmap through a method or property (as an image for example).
In general this is not typical.