Amlogic G12B hardware (inc. VIM3) has working H264, working 8-bit VP9 and working but imperfect HEVC decoding in the LE codebase and no support for 10-bit media or encoding. I run zero testing with conventional desktop OS like Ubuntu so cannot speak for how well our patchset might work in browsers or with WebRTC applications.
https://github.com/LibreELEC/LibreELEC.tv/ <= all sources (URLs or patches) are clearly listed here. If you want proper support and assistance with the upstream codebase I'd suggest you reach out to the Amlogic kernel maintainers at Baylibre who authored most of the drivers - who would love someone to fund more man-hours of development time so they can add more functionality and finish/polish features.