> And so far there is zero HW accelerated HEIF implementations for the web.
You sure of that? Apple[1] and Qualcomm[2] might argue otherwise.
[1] https://developer.apple.com/videos/play/wwdc2017/513/
[2] https://techreport.com/news/34306/qualcomm-snapdragon-855-sp...
Formats do not provide HW acceleration, implementations do. And so far there is zero HW accelerated HEIF implementations for the web.