It's interesting that hardware acceleration in browsers isn't necessarily the advantage you might thiink.
Modern CPUs have got very efficient with some codecs; even if they run around 100% on one core to decode 60fps 1080 content it's not necessarily heavy on the battery vs a GPU offload. In fact on my XPS13 I think it's about the same, but the heat's better when the CPU does the work.
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I've also seen similar on a Macbook Pro which runs 1080 nicely with no effort but stil uses about the same amount of battery power.
