From a2cb35148c40c39fce067dbb16c8694ee6afc557 Mon Sep 17 00:00:00 2001
From: Katherina Walshe-Grey <git@qenya.tel>
Date: Thu, 12 Sep 2024 11:38:17 +0100
Subject: [PATCH] pipewire-low-latency: split to reusable module

---
 hosts/kilgharrah/default.nix      |  2 ++
 services/default.nix              |  1 +
 services/pipewire-low-latency.nix | 58 +++++++++++++++++++++++++++++++
 3 files changed, 61 insertions(+)
 create mode 100644 services/pipewire-low-latency.nix

diff --git a/hosts/kilgharrah/default.nix b/hosts/kilgharrah/default.nix
index 6372b16..4418b4a 100644
--- a/hosts/kilgharrah/default.nix
+++ b/hosts/kilgharrah/default.nix
@@ -24,6 +24,8 @@
   console.keyMap = "uk";
   services.xserver.xkb.layout = "gb";
 
+  qenya.services.pipewire.lowLatency.enable = true;
+
   age.secrets.user-password-kilgharrah-qenya.file = ../../secrets/user-password-kilgharrah-qenya.age;
   users.users.qenya.hashedPasswordFile = config.age.secrets.user-password-kilgharrah-qenya.path;
   users.users.qenya.extraGroups = [ "wheel" ];
diff --git a/services/default.nix b/services/default.nix
index beecd73..fddd93c 100644
--- a/services/default.nix
+++ b/services/default.nix
@@ -1,5 +1,6 @@
 {
   imports = [
     ./forgejo.nix
+    ./pipewire-low-latency.nix
   ];
 }
\ No newline at end of file
diff --git a/services/pipewire-low-latency.nix b/services/pipewire-low-latency.nix
new file mode 100644
index 0000000..0ba2709
--- /dev/null
+++ b/services/pipewire-low-latency.nix
@@ -0,0 +1,58 @@
+{ config, lib, pkgs, ... }:
+
+let
+  inherit (lib) mkIf mkEnableOption;
+  cfg = config.qenya.services.pipewire.lowLatency;
+in
+{
+  options.qenya.services.pipewire.lowLatency = {
+    enable = mkEnableOption "config to decrease sound latency (increasing CPU load) for e.g. streaming";
+    # TODO: might be an idea to have the numbers be configurable
+  };
+
+  config = mkIf cfg.enable {
+    # TODO: needs more testing
+    services.pipewire.extraConfig = {
+      pipewire."92-low-latency" = {
+        context.properties = {
+          default.clock.rate = 48000;
+          default.clock.quantum = 32;
+          default.clock.min-quantum = 32;
+          default.clock.max-quantum = 32;
+        };
+      };
+      pipewire-pulse."92-low-latency" = {
+        context.modules = [
+          {
+            name = "libpipewire-module-protocol-pulse";
+            args = {
+              pulse.min.req = "32/48000";
+              pulse.default.req = "32/48000";
+              pulse.max.req = "32/48000";
+              pulse.min.quantum = "32/48000";
+              pulse.max.quantum = "32/48000";
+            };
+          }
+        ];
+        stream.properties = {
+          node.latency = "32/48000";
+          resample.quality = 1;
+        };
+      };
+    };
+    # Available from NixOS 24.11. Lifted from https://nixos.wiki/wiki/PipeWire - probably need to adjust numbers
+    # services.pipewire.wireplumber.extraLuaConfig.main."99-alsa-lowlatency" = ''
+    #   alsa_monitor.rules = {
+    #     {
+    #       matches = {{{ "node.name", "matches", "alsa_output.*" }}};
+    #       apply_properties = {
+    #         ["audio.format"] = "S32LE",
+    #         ["audio.rate"] = "96000", -- for USB soundcards it should be twice your desired rate
+    #         ["api.alsa.period-size"] = 2, -- defaults to 1024, tweak by trial-and-error
+    #         -- ["api.alsa.disable-batch"] = true, -- generally, USB soundcards use the batch mode
+    #       },
+    #     },
+    #   }
+    # '';
+  };
+}