Ember is so tired of people. 
nixos; aka "what documentation"
i was promised easy customisation of packages, not whatever this shit is
All I want to do is have configuration.nix compile ffmpeg with proper hw encoding support 
moved to @@Ember ffmpeg-full packages (like ffmpeg_6-full) should be able to cover this.
otherwise, you can enable specific codecs yourself with `(ffmpeg.override {build<Codec> = true; build<OtherCodec> = true; etc. etc.})`. a list of all the options is here: https://github.com/NixOS/nixpkgs/blob/nixos-unstable/pkgs/development/libraries/ffmpeg/generic.nix#L28
past that it might be an issue with something like vaapi, vdpau, nvenc, or whatever else you might be using for hardware accel
it seems i was being an idiot and the patch for vaapi av1 encoding just hasn't been merged into ffmpeg yet
@Ember ok so after a bit of tinkering it looks like this patch(set) is based on a specific version of ffmpeg - or at least one that is decently incompatible with the stable 6.0 release - so i think it would be a better idea to just compile from their repo instead of rebasing their patches or something. i made an override for ffmpeg_6-full here that does the basics with applying their patches and excluding some nixpkgs patches that are specific to 6.0. but i'm getting errors about 'VK_EXT_VIDEO_DECODE_H265_EXTENSION_NAME' not being found, but the encode equivalent is...and idk 
i don't think i have the experience with hacking at ffmpeg to figure this out, but hopefully i gave you a good start :p
@getchoo 
excuse my lack of knowledge in nix, but uh, how do i test this override?