PipeWire

PipeWire is a new low-level multimedia framework. It aims to offer capture and playback for both audio and video with minimal latency and support for PulseAudio-, JACK-, ALSA- and GStreamer-based applications. PipeWire has a great bluetooth support: because Pulseaudio was reported to have troubles with bluetooth, PipeWire can be a good alternative.

The daemon based on the framework can be configured to be both an audio server (with PulseAudio and JACK features) and a video capture server.

PipeWire also supports containers like Flatpak and does not rely on audio and video user groups but rather it uses a Polkit-like security model asking Flatpak or Wayland for permission to record screen or audio.

Enabling PipeWire

Add to your configuration:

# Remove sound.enable or turn it off if you had it set previously, it seems to cause conflicts with pipewire
#sound.enable = false;

# rtkit is optional but recommended
security.rtkit.enable = true;
services.pipewire = {
  enable = true;
  alsa.enable = true;
  alsa.support32Bit = true;
  pulse.enable = true;
  # If you want to use JACK applications, uncomment this
  #jack.enable = true;
};

The option definition services.pipewire.config no longer has any effect; overriding default Pipewire configuration through NixOS options never worked correctly and is no longer supported. Please create drop-in files in /etc/pipewire/pipewire.conf.d/ to make the desired setting changes instead. For example, you can create a file /etc/pipewire/pipewire.conf.d/pipewire.conf with the contents

context.properties = {
    log.level = 5
}

this will increase the log level to 5

Bluetooth Configuration

PipeWire can be configured to use specific codecs. The mSBC codec provides slightly better sound quality in calls than regular HFP/HSP, while the SBC-XQ provides better sound quality for audio listening. For more information see this link.

Wireplumber (services.pipewire.wireplumber) is the default modular session / policy manager for PipeWire in unstable, however there is currently no way to configure the advanced settings using the module. However, you can just drop the Lua files directly in the expected path (/etc/wireplumber/bluetooth.lua.d). For example:

environment.etc = {
	"wireplumber/bluetooth.lua.d/51-bluez-config.lua".text = ''
		bluez_monitor.properties = {
			["bluez5.enable-sbc-xq"] = true,
			["bluez5.enable-msbc"] = true,
			["bluez5.enable-hw-volume"] = true,
			["bluez5.headset-roles"] = "[ hsp_hs hsp_ag hfp_hf hfp_ag ]"
		}
	'';
};

If you want to change in your particular user instead of system-wide, you can add this to ~/.config/wireplumber/bluetooth.lua.d instead, manually or using Home-Manager.

If you're still on 21.11 or enabled pipewire-media-session manually (by setting services.pipewire.media-session.enable = true), them you can use the module to configure it:

services.pipewire  = {
  media-session.config.bluez-monitor.rules = [
    {
      # Matches all cards
      matches = [ { "device.name" = "~bluez_card.*"; } ];
      actions = {
        "update-props" = {
          "bluez5.reconnect-profiles" = [ "hfp_hf" "hsp_hs" "a2dp_sink" ];
          # mSBC is not expected to work on all headset + adapter combinations.
          "bluez5.msbc-support" = true;
          # SBC-XQ is not expected to work on all headset + adapter combinations.
          "bluez5.sbc-xq-support" = true;
        };
      };
    }
    {
      matches = [
        # Matches all sources
        { "node.name" = "~bluez_input.*"; }
        # Matches all outputs
        { "node.name" = "~bluez_output.*"; }
      ];
    }
  ];
};

Graphical tools

All protocols (Pulseaudio/JACK) are now talking to the PipeWire protocol and are managed by the PipeWire daemon (therefore, applications can be managed by both Pulseaudio and JACK tools). For that reason, all graphical tools used for these protocols can be used:

• pavucontrol: controls the volume (per-sink and per-app basis), the default outputs/inputs, the different profiles (for HDMI outputs/bluetooth devices), routes each application to a different input/output, etc.
• plasma-pa: a Plasma applet to change volume directly from the systray. Also deals with volume keys.
• qjackctl: with JACK emulation, provides a patchbay (to connect applications together). Note that JACK does not provide any way to change the volume of a single application; use Pulseaudio tools for that purpose.
• carla: with JACK emulation, provides a patchbay (make sure to go to "Patchbay" tab and check "Canvas > Show External").
• catia/patchage: similar to qjackctl and carla.
• Helvum: GTK-based patchbay for PipeWire (uses the PipeWire protocol). Volume control is planned for later.

Advanced Configuration

PipeWire can be extensively configured to fit the users' needs. Should the user want to do some fancy routing with null sinks, these can be defined directly in the config as shown below.

This is especially convenient if the user has a multi-channel (8+, or something "weird" like 2x2, 3x2) soundcard that keeps confusing applications with too many channels or a bad channel layout.

Note: those cards can be set to the "Pro Audio" profile with pavucontrol so PipeWire doesn't try to guess a wrong channel layout for them.

environment.etc = let
  json = pkgs.formats.json {};
in {
  "pipewire/pipewire.d/91-null-sinks.conf".source = json.generate "91-null-sinks.conf" {
    context.objects = [
      {
        # A default dummy driver. This handles nodes marked with the "node.always-driver"
        # properyty when no other driver is currently active. JACK clients need this.
        factory = "spa-node-factory";
        args = {
          factory.name     = "support.node.driver";
          node.name        = "Dummy-Driver";
          priority.driver  = 8000;
        };
      }
      {
        factory = "adapter";
        args = {
          factory.name     = "support.null-audio-sink";
          node.name        = "Microphone-Proxy";
          node.description = "Microphone";
          media.class      = "Audio/Source/Virtual";
          audio.position   = "MONO";
        };
      }
      {
        factory = "adapter";
        args = {
          factory.name     = "support.null-audio-sink";
          node.name        = "Main-Output-Proxy";
          node.description = "Main Output";
          media.class      = "Audio/Sink";
          audio.position   = "FL,FR";
        };
      }
    ];
  };
};

Linking nodes

The config does not currently cover linking nodes together, but this can be fixed with a script. Soundcard names and ports should be replaced with the ones from the user's configuration:

#!/usr/bin/env bash

# ports obtained from `pw-link -io`

pw-link "Main-Output-Proxy:monitor_FL" "alsa_output.usb-Native_Instruments_Komplete_Audio_6_69BC86B9-00.pro-audio:playback_1"
pw-link "Main-Output-Proxy:monitor_FR" "alsa_output.usb-Native_Instruments_Komplete_Audio_6_69BC86B9-00.pro-audio:playback_2"

pw-link "alsa_input.usb-M-Audio_Fast_Track-00.pro-audio:capture_1" "Microphone-Proxy:input_MONO"

In order to load the script on startup, it can be added to ~/.xprofile or the specific DE/WM autostart config. Similarly, a one-shot user service can be created that runs the script.

Low-latency setup

Audio production and rhythm games require lower latency audio than general applications. PipeWire can achieve the required latency with much less CPU usage compared to PulseAudio, with the appropriate configuration. The minimum period size controls how small a buffer can be. The lower it is, the less latency there is. PipeWire has a value of 32/48000 by default, which amounts to 0.667ms. It can be brought lower if needed:

environment.etc = let
  json = pkgs.formats.json {};
in {
  "pipewire/pipewire.d/92-low-latency.conf".source = json.generate "92-low-latency.conf" {
    context.properties = {
      default.clock.rate = 48000;
      default.clock.quantum = 32;
      default.clock.min-quantum = 32;
      default.clock.max-quantum = 32;
    };
  };
};

NOTE: Every setup is different, and a lot of factors determine your final latency, like CPU speed, RT/PREEMPTIVE kernels and soundcards supporting different audio formats. That's why 32/48000 isn't always a value that's going to work for everyone. The best way to get everything working is to keep increasing the quant value until you get no crackles (underruns) or until you get audio again (in case there wasn't any). This won't guarantee the lowest possible latency, but will provide a decent one paired with stable audio.

PulseAudio backend

Applications using the Pulse backend have a separate configuration. The default minimum value is 1024, so it needs to be tweaked if low-latency audio is desired.

environment.etc = let
  json = pkgs.formats.json {};
in {
  "pipewire/pipewire-pulse.d/92-low-latency.conf".source = json.generate "92-low-latency.conf" {
    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;
    };
  };
};

As a general rule, the values in pipewire-pulse should not be lower than the ones in pipewire.

Controlling the ALSA devices

It is possible to configure various aspects of soundcards through PipeWire, including format, period size and batch mode:

environment.etc.
"wireplumber/main.lua.d/99-alsa-lowlatency.lua".text = ''
  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
      },
    },
  }
'';

The matches attribute applies the actions to the devices/properties listed there. It is usually used with soundcard names, like shown in the config above. <matches> can match any of the outputs of

$ pw-dump | grep node.name | grep alsa

Troubleshooting

Volume keys do not work in KDE, and sound applet is gone

If volume keys do not work in KDE and/or you don't have the sound applet, make sure to install `plasma-pa` (you may need to restart the session for it to apply). Now added automatically thanks to this PR (22/05/2021).

pactl not found

If you want to use some Pulseaudio commands like pactl, you can safely install (either systemwide or in a nix-shell) the `pulseaudio` package (do not enable it in the system configuration). The pactl functionality is superseded in PipeWire with the native pw-cli, pw-mon and pw-top CLI tools. When using WirePlumber (which is enabled by default), you can also use wpctl as a pactl alternative with similar high level subcommands.

See also

• https://github.com/NixOS/nixpkgs/issues/102547