Chromiun now supports upstream Linux V4L2 stateless decoders along side the ChromeOS specific APIs, as well as the stateful codecs.
From the rpmfusion bug report:
This is a feature request, I am willing to help with the actual work if with some pointers (as I don't know were to start). Chromium Freeworld package enables VAAPI HW decoding which is great of Intel/AMD platforms, but I'd like to have a HW accelerated browsers on Raspberry Pi, Rockchip RK3399 and more.
Chromium have support for this, though it has to be compiled in. This is used on ChromeOS ARM Chromebook. There is in fact 2 type of CODECs, stateful and stateless. The stateful one will enable H264 on Raspberry Pi, but also enable SoC running Qualcomm Venus driver, Amlogic CODECs, etc.
The stateless situation was a bit in flux until now, as Chromium was implementing few downstream kernel API and did not have support for the final uAPI yet. This situation is fixed now, so support for final uAPI for H.264, VP8 and VP9 is now available.
Note we already enable the Linux v4l2 interfaces as well as the appropriate drivers.
So in theory all that should be needed is the following addition to the spec but it fails and I don't understand the Chromium builds well enough:
Got slightly more info today, there is a CL from Wens to op-out any downstream uAPI support in linux builds.
Though he said that there might be some issues related to some downstream GBM deps they have (to be confirmed).