

Blowing Up HTML5 Video and Mapping It into 3d Space (2010) - flavioribeiro
http://www.craftymind.com/blowing-up-html5-video-and-mapping-it-into-3d-space/

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"Don’t ask me why, but copying pixel data out of a video tag is expensive"

I'd bet good money that is because it has to switch to a software RGB system-
memory-backed indirect rendering path, bypassing all the acceleration provided
by modern GPUs, whether that is on-GPU H.264 decoding, or just YCrCb
colorspace conversion, or any of the other tricks that standard 2d video
players pull off. Or it might even try to do the full HW path and then read
back RGB "in the opposite direction" from the final framebuffer which would be
even slower.

