highascg

Audio setup guide (CasparCG on Ubuntu)

Single entry point for multi-channel playout: follow one path below, then use Audio routing reference for MIXER / route:// / FFmpeg mapping details.

Related: WO-06 Audio playout · Phase 5 (T5.1)

Topic	Deep dive
List ALSA devices	ALSA device enumeration
NVIDIA HDMI/DP, 3.5 mm, USB	Caspar outputs: NVIDIA, stereo, USB
Consumers in casparcg.config	Caspar audio consumers
AES67, Dante bridges, NDI tools, NetJACK, ROC	Network audio protocols
PipeWire sinks / graph	PipeWire multi-channel routing
JACK alternative	JACK audio routing

---

Before you start

1. Sample rate: Caspar channels typically run at 48 kHz; FFmpeg -ar 48000 and hardware must agree.
2. Layout vs hardware: channel-layout on the channel (and any custom names in <audio><channel-layouts>) must match what you send with -ac and what the sink can play.
3. Find hw:N,M: aplay -l (see enumeration doc). HighAsCG can list devices via GET /api/audio/devices when the app runs on the same machine as Caspar.

---

1. NVIDIA HDMI / DisplayPort

Goal: Send program audio over the GPU’s digital audio device (often 2–8 channels on one link).

1. Confirm driver: lsmod | grep snd_hda_intel (see §1.1).
2. Map the connector: aplay -l | grep -iE 'nvidia|hdmi|display' → note card and device → hw:N,M.
3. Test: aplay -D hw:N,M /usr/share/sounds/alsa/Front_Center.wav (or any short WAV).
4. Multi-channel: speaker-test -D hw:N,M -c 8 if you need to validate >2ch (see enumeration doc).
5. Caspar: add FFmpeg consumer with -f alsa hw:N,M and -ac / codec matching your layout, or <system-audio/> if the default desktop sink should follow HDMI (less deterministic on headless servers).

Also read: §1.6 — HDMI/DP into a video switcher (embedded audio into switchers that de-embed / bridge to Dante).

---

2. USB audio interface

Goal: Class-compliant multi-channel output (often 8–32+ channels).

1. Plug in the interface; aplay -l should show the product name on a USB card.
2. Match rate and channel count to the device spec (see §3).
3. Probe channels: speaker-test -D hw:N,M -c 8 (adjust -c).
4. Caspar: FFmpeg consumer -f alsa hw:N,M with -codec:a pcm_s16le or pcm_s24le, -ar 48000, -ac N.

Dante on the network: Linux has no Dante Virtual Soundcard; use a USB–Dante hardware bridge or AES67 mode — Network audio protocols § T3.1.

---

3. AES67 / Dante bridge

Goal: Get audio into a Dante domain without DVS on Linux.

1. Prefer a hardware bridge (e.g. USB interface with Dante ports): it appears as ALSA on Linux; route Caspar FFmpeg to hw:N,M like any USB device.
2. AES67 mode on Dante endpoints: configure in Dante Controller (Windows/Mac), then use a Linux AES67/RAVENNA stack or PipeWire module as described in § T3.1.

---

4. NDI (network)

Goal: Send video + embedded audio to the LAN.

1. Enable NDI consumer on the Caspar channel; set <name> uniquely (§ T2.3).
2. Downstream: NDI Studio Monitor, FFmpeg with libndi_newtek, or hardware — § T3.2.

---

5. PipeWire multi-channel routing

Goal: Virtual sinks, graph routing, or ROC — when a single hw: device is not enough.

1. Install PipeWire + WirePlumber (default on recent Ubuntu).
2. Optional: drop-in clock/quantum under /etc/pipewire/pipewire.conf.d/ (PipeWire doc).
3. Create null-sinks or named sinks for each Caspar “bus”; point Caspar FFmpeg to -f pulse sink_name.
4. Use qpwgraph to verify edges from Caspar’s process to the right sink.

---

Troubleshooting

Symptom	Things to check
No sound	Wrong hw:N,M; cable/port; monitor/switcher input selected; PULSE_SINK / default sink for <system-audio/>.
Only 2 channels work	Layout is stereo but you need 8ch / custom; HDMI EDID limits; -ac too small.
Crackle / xruns	Increase buffer (-buffer_size in FFmpeg args, or PipeWire quantum); avoid competing exclusive hw users.
Device busy	Another app holds ALSA hw exclusively; use Pulse/PipeWire path or stop the other app.
Dante not in OS	Expected on Linux without a bridge — use AES67 + Linux stack or USB–Dante hardware.

Diagnostic commands

aplay -l
pactl list short sinks          # PipeWire/Pulse sinks
pw-cli list-objects Node       # PipeWire nodes (best-effort)
speaker-test -D hw:N,M -c N

---

HighAsCG settings

Application Settings → Audio / OSC stores audioRouting (program layout, ALSA/NDI/system/custom FFmpeg, extra buses). The config generator merges this into flat Caspar keys — see src/config/config-generator.js (mergeAudioRoutingIntoConfig).

This site is open source. Improve this page.