[maggit]

It looks like it implements hardware acceleration of the VP9 codec for some specific hardware (Rockchip VDEC and Hantro G2). This opens up playing, for example, lots of YouTube videos with less CPU usage on devices with that hardware. I can't comment on whether or not it "took so long" as I have no idea which hardware this is.

The title makes it out to be something fundamental in Linux, but this is just one driver becoming more complete.

[megous]

It's a new media subsystem userspace API, not just a new driver, and the API will be stable from the get go, instead of languishing in the staging area, like the H.264 one.

[CameronNemo]

Is the h264 one going to move out of staging anytime soon?