[cylemons]

How does testing rendering work? Can javascript get pixel data from the DOM

[Beretta_Vexee]

https://www.w3schools.com/tags/canvas_getimagedata.asp

[cylemons]

So the way this works is to draw fonts/svgs inside the canvas and check the pixels, that makes sense

[Beretta_Vexee]

This is just one element among many others. They probably have many available and others in reserve in case one becomes obsolete.

I recently discovered that audio codecs, frequencies, resolution, mix volume, etc. are accessible via JS in the browser and that this allows fingerprinting. Since we are talking about YouTube, the same type of technique should be possible with video codecs.