improve obs-v4l2sink

[notpeelz]

Motivation for this change

I started working on my own derivation of obs-v42lsink and realized that it had been added to nixpkgs 4 days ago. So I compared the two derivations and noticed a couple things that were done differently.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

@grahamc @colemickens

[notpeelz]

Related PR: #84153

@grahamc @colemickens

[cole-h]

@ofborg eval

GitHub seems to be recover(ing/ed).

[notpeelz]

The 32-bit derivation can be tested with this:

{ pkgs ? import ./nixpkgs {}, is32bit ? false }:

with pkgs.lib;
let
  deps = pkgs: {
    inherit (pkgs)
      obs-studio
      obs-v4l2sink;
  };
  depsAttrset = if is32bit
    then deps pkgs.pkgsi686Linux.pkgs
    else deps pkgs;
in pkgs.stdenv.mkDerivation {
  name = "env";
  buildInputs = attrValues depsAttrset;
  shellHook = ''
    echo "obs-studio: ${depsAttrset.obs-studio.outPath}"
    echo "obs-v4l2sink: ${depsAttrset.obs-v4l2sink.outPath}"
    ln -sfT \
      ${depsAttrset.obs-v4l2sink}/share/obs/obs-plugins/v4l2sink \
      ~/.config/obs-studio/plugins/v4l2sink
  '';
  unpackPhase = ":";
  installPhase = "touch $out";
}

$ nix-shell --arg is32bit true

[colemickens]

(Mentioned in IRC, but just for continuity's sake, including here.)

I applied this patch which made the directory structure back to what home-manager expects (and what other plugins tend to follow):

diff --git a/pkgs/applications/video/obs-studio/v4l2sink.nix b/pkgs/applications/video/obs-studio/v4l2sink.nix
index 29479a33a1b..eddb7928d85 100644
--- a/pkgs/applications/video/obs-studio/v4l2sink.nix
+++ b/pkgs/applications/video/obs-studio/v4l2sink.nix
@@ -35,8 +35,8 @@ stdenv.mkDerivation rec {
   }.${stdenv.targetPlatform.system} or (throw "Unsupported system: ${stdenv.targetPlatform.system}");
 
   postInstall = ''
-    mkdir -p $out/$pluginPath
-    ln -s $out/lib/obs-plugins/v4l2sink.so $out/$pluginPath
+    mkdir -p $out/share/obs/obs-plugins/v4l2sink/$pluginPath
+    ln -s $out/lib/obs-plugins/v4l2sink.so $out/share/obs/obs-plugins/v4l2sink/$pluginPath
   '';
 
   meta = with lib; {

[colemickens]

Okay, I can confirm - this doesn't crash on Stop anymore. Thanks, looks good.

[jtojnar]

Why is this needed? Could you add a comment?

[notpeelz]

obs-studio seems to expects a specific directory structure for plugins, otherwise it won't find it.

[jtojnar]

Is that upstream thing or our packaging thing. If the former, why does the project not already do that?

Either way, the comment should be part of the expression.

[notpeelz]

It's an upstream thing. It looks for plugins in $XDG_CONFIG_HOME/obs-studio/plugins and /usr/share/obs/obs-plugins.

Comment added.

[jtojnar]

The path shenanigans are weird, looks good otherwise.

[colemickens]

Pulled latest commits as of right now - still works in my HM-managed setup. LGTM thanks!

[jtojnar]

Thanks.

[grahamc]

coming back to this PR for instructions on how to "install" the plugin. Gosh, I would so love a obs-studioWithPlugins

[notpeelz]

Yeah that would be a good idea. For now I just have home-manager create a symlink to ${obs-v4l2sink}/share/obs/obs-plugins/v4l2sink in ~/.config/obs-studio/plugins.

[colemickens]

From my nixcfg: home-manager makes it easy:

    home-manager.users.cole = { pkgs, ... }: {
      programs = {
        obs-studio = {
          enable = true;
          plugins = with pkgs; [ obs-wlrobs obs-v4l2sink ];
        };
      };
    };

[Algram]

@colemickens Hi, thanks for that example! It helped me a lot. Can I ask how you manage the v4l2loopback module that is required in order for the obs-v4l2sink plugin to work?

[davidak]

@Algram good question. i got the module loaded and exclusive_caps enabled with

  boot.extraModulePackages = [ pkgs.linuxPackages_latest.v4l2loopback ];
  boot.kernelModules = [ "v4l2loopback" ];
  boot.extraModprobeConfig = ''
    options v4l2loopback exclusive_caps=1 video_nr=9 card_label="obs"
  '';

#84153 (comment)

together with the home-manager from #85690 (comment) it works!

It would be nice to have documentation for this!