Audio Pipewire

Audio PipeWire

Context: $ARGUMENTS

Quick start

• List audio graph objects: → Step 1 (pwctl.py list)
• Dump the whole graph as JSON: → Step 2 (pwctl.py dump)
• Render a compact ASCII graph: → Step 2 (pwctl.py graph)
• Connect app A → device B: → Step 3 (pwctl.py link <src> <dst>)
• Play / record a file: → Step 4 (pwctl.py play / record)
• Create a virtual cable (loopback): → Step 5 (pwctl.py loopback)
• Watch DSP load / xruns: → Step 6 (pwctl.py top)
• Change default sink/source: → Step 7 (pwctl.py metadata-set)

When to use

• User is on Linux and wants to route audio between apps or devices.
• User asks about PipeWire, pw-* commands, or WirePlumber.
• User needs to list/filter nodes and ports, create port-level links, or set the default sink/source.
• User asks how to create a virtual audio device on Linux — use pw-loopback.
• User wants to debug audio latency or xruns on Linux.

Not for: macOS (use audio-coreaudio), Windows (use audio-wasapi), or JACK-specific workflows (use audio-jack — but note that on modern Linux, jackd is almost always the PipeWire libjack shim anyway).

Step 1 — List objects

Probe the current graph for every node/port/link/device/module/metadata object:

uv run ${CLAUDE_SKILL_DIR}/scripts/pwctl.py list

Filter by type (keeps output manageable on busy desktops):

uv run ${CLAUDE_SKILL_DIR}/scripts/pwctl.py list --kind Node
uv run ${CLAUDE_SKILL_DIR}/scripts/pwctl.py list --kind Port
uv run ${CLAUDE_SKILL_DIR}/scripts/pwctl.py list --kind Link

For the full object-type taxonomy see references/elements.md.

Step 2 — Dump / graph

Full JSON snapshot of every object, matching the output format that pw-dump itself produces:

uv run ${CLAUDE_SKILL_DIR}/scripts/pwctl.py dump

Stream live updates (useful when diagnosing a node that appears only when an app is launched):

uv run ${CLAUDE_SKILL_DIR}/scripts/pwctl.py dump --monitor

Client-side substring filter:

uv run ${CLAUDE_SKILL_DIR}/scripts/pwctl.py dump --filter firefox

Compact ASCII rendering (nodes on the left, their outgoing links on the right):

uv run ${CLAUDE_SKILL_DIR}/scripts/pwctl.py graph
uv run ${CLAUDE_SKILL_DIR}/scripts/pwctl.py graph --kind audio   # audio links only

Step 3 — Link / unlink ports

pw-link operates at the port level. Each audio node has one port per channel. To bridge stereo Firefox → Scarlett playback front-left/front-right:

uv run ${CLAUDE_SKILL_DIR}/scripts/pwctl.py link 'Firefox:output_FL' 'alsa_output.usb-Focusrite_Scarlett:playback_FL'
uv run ${CLAUDE_SKILL_DIR}/scripts/pwctl.py link 'Firefox:output_FR' 'alsa_output.usb-Focusrite_Scarlett:playback_FR'

List existing links:

uv run ${CLAUDE_SKILL_DIR}/scripts/pwctl.py links

Remove a link:

uv run ${CLAUDE_SKILL_DIR}/scripts/pwctl.py unlink 'Firefox:output_FL' 'alsa_output.usb-Focusrite_Scarlett:playback_FL'

You can pass numeric object ids (from list) instead of names.

Step 4 — Play / record files

pw-cat is the unified playback+record tool. pw-play/pw-record are symlinks:

uv run ${CLAUDE_SKILL_DIR}/scripts/pwctl.py play path/to/track.wav
uv run ${CLAUDE_SKILL_DIR}/scripts/pwctl.py play path/to/track.wav --target alsa_output.usb-...
uv run ${CLAUDE_SKILL_DIR}/scripts/pwctl.py record captured.wav --duration 10

record is implemented as pw-cat --record. PipeWire negotiates format from the file extension (WAV / FLAC / RAW). For MIDI use pw-midiplay / pw-midirecord directly (not wrapped here — they take SMF files).

Step 5 — Loopback (virtual cable)

pw-loopback creates a virtual source↔sink pair that any app can target. Classic use case: capture system audio into OBS by recording from the loopback source.

uv run ${CLAUDE_SKILL_DIR}/scripts/pwctl.py loopback --name MyVirtualCable --channels 2

Bridge specific endpoints:

uv run ${CLAUDE_SKILL_DIR}/scripts/pwctl.py loopback \
  --name StreamMix \
  --capture 'alsa_input.usb-...' \
  --playback 'alsa_output.usb-...'

pw-loopback runs in the foreground; kill with SIGINT when done. To make one permanent, add a module fragment under ~/.config/pipewire/pipewire.conf.d/ or a WirePlumber Lua script.

Step 6 — Watch DSP load / xruns

uv run ${CLAUDE_SKILL_DIR}/scripts/pwctl.py top                     # curses TUI
uv run ${CLAUDE_SKILL_DIR}/scripts/pwctl.py top --batch-mode --iterations 5

Columns: S(tate), id, QUANTum, RATE, WAIT, BUSY, W/Q (wait/quantum%), B/Q (busy/quantum%), ERR (xruns), FORMAT, NAME.

Rule of thumb: if B/Q > ~70% a node can't keep up with its quantum; drop quantum or raise the period.

Step 7 — Metadata (default sink/source)

pw-metadata reads/writes the shared metadata store. WirePlumber and pipewire-pulse both consult it.

Read the current defaults:

uv run ${CLAUDE_SKILL_DIR}/scripts/pwctl.py metadata-get --id 0

Change the default audio sink (note the JSON-wrapped value — WirePlumber requires it):

uv run ${CLAUDE_SKILL_DIR}/scripts/pwctl.py metadata-set \
  --id 0 --key default.configured.audio.sink \
  --value '{ "name": "alsa_output.usb-Focusrite_Scarlett" }' \
  --type Spa:String:JSON

To see WirePlumber's config search paths (where to drop a Lua fragment to persist changes):

uv run ${CLAUDE_SKILL_DIR}/scripts/pwctl.py wireplumber-config

Gotchas

• WirePlumber is the current session manager. pipewire-media-session is deprecated and won't match the behavior of a current WirePlumber-based distro. Don't look up Lua/Spa-Json config against the old media-session docs.
• PipeWire's jackd shim vs real JACK. On most modern Linux desktops the jackd binary on $PATH is PipeWire's libjack shim — starting it a second time does not change quantum/period/samplerate. To raise/lower quantum under PipeWire use pw-metadata -n settings 0 clock.force-quantum <N> (set 0 to let WirePlumber pick).
• Port names can contain spaces, colons, and dots. Always quote them. pw-link "node name:port name" "other:port". Numeric ids are safer for scripts.
• Channel layout mismatch refuses to link. Linking a mono source to a stereo sink needs two explicit port-level links (or a channelmap/loopback). PipeWire won't auto-broadcast.
• pw-dump without --monitor is a snapshot, not a live stream. For an app that only creates its nodes on startup, run --monitor and then launch the app.
• pw-cat --record does not take --duration. This wrapper wraps with timeout to bound a recording. Without it, record until SIGINT.
• Changing default sink via pw-metadata only persists if WirePlumber policy saves it. For true persistence, add a WirePlumber Lua fragment under ~/.config/wireplumber/main.lua.d/.
• pw-loopback exits as soon as you interrupt it. For persistent virtual cables, load the libpipewire-module-loopback module from a config fragment instead of running the CLI.
• pw-top measures graph time, not CPU %. A B/Q near 100% means "this node is burning almost all of its scheduled quantum", which may or may not be the CPU bottleneck.
• Object IDs change between daemon restarts. Hardcode node names (e.g. alsa_output.usb-Focusrite_Scarlett) in scripts, not ids.
• Metadata JSON values need the Spa:String:JSON type hint. Plain strings don't deserialize — WirePlumber will silently ignore the write.
• pw-jack <app> vs jackd. pw-jack firefox launches Firefox against PipeWire's libjack shim for the process only — useful for testing JACK apps without replacing system jackd.

Examples

Example 1 — "Route Firefox to my USB interface"

uv run ${CLAUDE_SKILL_DIR}/scripts/pwctl.py list --kind Port      # find port names
uv run ${CLAUDE_SKILL_DIR}/scripts/pwctl.py link 'Firefox:output_FL' 'alsa_output.usb-Focusrite_Scarlett:playback_FL'
uv run ${CLAUDE_SKILL_DIR}/scripts/pwctl.py link 'Firefox:output_FR' 'alsa_output.usb-Focusrite_Scarlett:playback_FR'

Example 2 — "Capture system audio for OBS"

uv run ${CLAUDE_SKILL_DIR}/scripts/pwctl.py loopback --name OBS_Cable --channels 2
# Point OBS's "Audio Input Capture" at OBS_Cable, then route apps to it:
uv run ${CLAUDE_SKILL_DIR}/scripts/pwctl.py link 'Firefox:output_FL' 'OBS_Cable:input_FL'
uv run ${CLAUDE_SKILL_DIR}/scripts/pwctl.py link 'Firefox:output_FR' 'OBS_Cable:input_FR'

Example 3 — "My audio keeps dropping; is it xruns?"

uv run ${CLAUDE_SKILL_DIR}/scripts/pwctl.py top --batch-mode --iterations 20
# Look at the ERR column. Then raise the quantum:
pw-metadata -n settings 0 clock.force-quantum 1024

Example 4 — "List every link in the graph"

uv run ${CLAUDE_SKILL_DIR}/scripts/pwctl.py links

Example 5 — "Change default sink"

uv run ${CLAUDE_SKILL_DIR}/scripts/pwctl.py metadata-set \
  --id 0 --key default.configured.audio.sink \
  --value '{ "name": "alsa_output.usb-Focusrite_Scarlett" }' \
  --type Spa:String:JSON

Troubleshooting

Error: pw-cli: command not found / pw-link: command not found

Cause: PipeWire is not installed or $PATH missing. Fix: Install the distro package (Fedora: pipewire, pipewire-utils; Debian/Ubuntu: pipewire-bin, wireplumber). Confirm with pw-cli --version.

pw-link exits with "port not found"

Cause: Port name string doesn't match, or the source/sink doesn't exist yet. Fix: Run pwctl.py list --kind Port to see the exact names. Quote shell-special chars. Or pass numeric ids from list.

pw-dump returns empty []

Cause: PipeWire daemon not running under the current session. On some minimal installs the service isn't autostarted. Fix: systemctl --user start pipewire.service pipewire-pulse.service wireplumber.service and retry.

Loopback disappears after logout

Cause: pw-loopback CLI is tied to the foreground process. Fix: Persist via libpipewire-module-loopback in a config fragment under ~/.config/pipewire/pipewire.conf.d/, or a WirePlumber Lua fragment.

Default sink resets on reboot

Cause: WirePlumber's default-nodes.lua did not persist the change. Fix: Write a Lua persistence fragment under ~/.config/wireplumber/main.lua.d/ instead of relying solely on pw-metadata.

Reference docs

• Object/type taxonomy (Node, Port, Link, Device, Module, Metadata) and common property keys → references/elements.md.