Amlogic and Allwinner SoCs have varying degrees up media decode support in mainline kernels (h264 is supported, other codecs vary). Armbian supports a bunch of such boards with Linux 5.3. What exactly are you trying to do?

We're building libre streaming hardware for https://fosdem.org .

Our current approach is using the Allwinner A20 processor. Investing quite a bit of work in a free driver for the h264 encoding block on there (cedrus vpu).

It was an honest question if we had overlooked something obvious...

Yeah, the Cedrus VPU is already supported upstream: https://linux-sunxi.org/Sunxi-Cedrus

That page is a bit out of date, I think the support has improved since then.

I've not used them. YMMV. But they seem to match your description.