jernej

That is default fallback resolution when kernel can't read resolution info from display (on all platforms and architectures). There can be multiple reasons, like cable, monitor, some kernel/driver issue...

Your understanding is incorrect: 1. VDPAU was used only with vendor kernel, which is obsolete for a long time. Armbian uses only mainline kernel. 2. No need to worry due to 1) 3. GPU doesn't do anything for video decoding. That's desktop PC concept. Embedded SoCs have dedicated VPUs (video processing unit). But it's true that ffmpeg need patching. More specifically, it needs v4l2 request api support. 4. That's not necessary if ffmpeg libraries are patched and installed system wide. Last but not least, v4l2 request video decoding support is tested only in Kodi GBM mode. This means that it must be started from console, when no desktop environment is running. Maybe wayland mode would work, but I don't know. Certainly it won't work under X11. You have to use software decoding there.

AFAIK, mainline kernel isn't meant to be booted in secure mode and this is just to allow BSP kernel to be booted. I might be wrong, though. Just try running in non-sec mode.

That's not true anymore. MPV support it via GPU rendering in v0.35 for both, X and Wayland. However, you still need patched ffmpeg for that.

yes

Latest stable version of mpv also supports video playback with patched ffmpeg, even in x11 and wayland. If Armbian would package such ffmpeg, it would make almost trivial for people to watch movies using mpv on desktop.

It has nothing to do with video decoding. Read posts right before yours.

NV15, although sounds standard, it's not. It's RK invention and used only (AFAIK) on their chips. So I would presume not many mesa developers are aware of it and even less care about it. Note, EGL has nothing to do with DRM planes. EGL lists format supported for GPU rendering and DRM planes lists formats supported by Direct to plane rendering. There is catch, though. ffmpeg must provide proper mapping to DRM descriptor. I have no idea if that's done for NV15 in ffmpeg rkmpp module. If that's not done, direct to plane method won't work. Note that I don't care about vendor solutions and I'm only indirectly involved with RK platforms, so I can't help you more.

Driver needs a bit of rework since Cedrus on H6 needs a bit different initialization. I guess you need this for video encoding?