Why VP8 and VP9 aren't hardware accelerated?
“Our goal is to have a Stable and secure browser first, and a GPU-accelerated one second, when possible. As we found out time and again, any sort of GPU acceleration has a lot of maintenance associated with it, between the multitude of configurations our users run, the general lack of quality of drivers (in particular on Linux), and the constant stream of incoming issue due to new hardware, driver, or distribution release.”
These bugs are about video acceleration as whole, not specifically about VP8/9. If Chromium doesn't use GPU on Linux, then h264 will be eating CPU as well.