Audio: select the output device (fixes silent output on Raspberry Pi)

The player always opened the system default output device. On a
Raspberry Pi that default is often HDMI, so playback ran but nothing
came out of the headphone jack or a USB/DAC -- "it plays but I hear no
sound".

Add an [audio] device option to crabidy-server.toml: a case-insensitive
substring of the output device name (a memorable fragment is enough).
The player engine opens the first matching device and falls back to the
system default with a warning if none matches. Absent config keeps the
system default, so existing setups are unchanged.

To discover the names, a new `crabidy-server audio-devices` subcommand
(also on `cbd`) lists the output devices and marks the one the current
config selects, using the same match the server applies at startup.

Plumbing: audio_player::output_device_names() enumerates via cpal;
Player::new(Option<String>) replaces the device-less construction
(Default = new(None)); Playback::new takes the device and serve() reads
it from settings. cpal's name() is deprecated in favor of description(),
but name() returns the ALSA-stable string users see in `aplay -l` and
match against, so it is kept behind a documented #[allow(deprecated)].

README documents the [audio] device option under the Pi/config section.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

README.md

@@ -157,6 +157,32 @@ startup rather than silently running open. Note that the transport is
 plain HTTP/2: fine on a trusted home network, but anything exposed
 further needs TLS termination (reverse proxy, VPN) in front.
 
+#### Audio output device
+
+By default the server plays to the system default output device. On a
+Raspberry Pi that is often HDMI, so playback runs but you hear nothing on
+the headphone jack or a USB/DAC. List the devices the server can see:
+
+```console
+$ crabidy-server audio-devices
+Audio output devices (* = selected by the current config):
+    hdmi:CARD=vc4hdmi,DEV=0
+    sysdefault:CARD=Headphones
+    ...
+```
+
+Then pin one in `crabidy-server.toml` — the value is matched
+case-insensitively as a substring of the name, so a memorable fragment is
+enough — and restart the server:
+
+```toml
+[audio]
+device = "Headphones"
+```
+
+If the name matches nothing, the server logs a warning and falls back to
+the system default.
+
 ## Command line
 
 Every binary is a clap CLI: run it with `--help` (and any subcommand

audio-player/src/lib.rs

@@ -4,5 +4,5 @@ mod spectrum_tap;
 pub mod windowed_http;
 
 pub use player::{Player, PlayerError};
-pub use player_engine::{MediaInfo, PlayerMessage};
+pub use player_engine::{output_device_names, MediaInfo, PlayerMessage};
 pub use spectrum_tap::{SpectrumTap, SPECTRUM_WINDOW};

audio-player/src/player.rs

@@ -22,6 +22,16 @@ pub struct Player {
 
 impl Default for Player {
     fn default() -> Self {
+        Self::new(None)
+    }
+}
+
+impl Player {
+    /// Spawns the player engine on its own thread, sending audio to the
+    /// output device whose name contains `device` (case-insensitive), or the
+    /// system default when `device` is `None`. See
+    /// [`crate::output_device_names`] to discover names.
+    pub fn new(device: Option<String>) -> Self {
         let (tx_engine, rx_engine) = flume::bounded(16);
         let (tx_player, messages): (Sender<PlayerMessage>, Receiver<PlayerMessage>) =
             flume::bounded(16);
@@ -36,7 +46,8 @@ impl Default for Player {
         let spectrum = SpectrumTap::new();
         let engine_tap = spectrum.clone();
         thread::spawn(move || {
-            let engine = match PlayerEngine::init(tx_callbacks, tx_player, runtime, engine_tap) {
+            let engine =
+                match PlayerEngine::init(tx_callbacks, tx_player, runtime, engine_tap, device) {
                     Err(e) => {
                         error!("Could not initialize player: {}", e);
                         return;
@@ -52,9 +63,7 @@ impl Default for Player {
             spectrum,
         }
     }
-}
 
-impl Player {
     /// The spectrum tap the played audio is mirrored into.
     pub fn spectrum_tap(&self) -> Arc<SpectrumTap> {
         self.spectrum.clone()

audio-player/src/player_engine.rs

@@ -107,15 +107,78 @@ pub struct PlayerEngine {
     pre_mute_volume: f32,
 }
 
+/// The names of the available audio output devices, best-effort (an empty
+/// list if the host cannot be queried). Shown by `crabidy-server
+/// audio-devices` so a user can pick one for the `[audio] device` config.
+//
+// `DeviceTrait::name` is deprecated in cpal 0.17 in favor of `description()`,
+// but on the ALSA backend (the Raspberry Pi target) `name()` returns the
+// stable device string users already see in `aplay -l` and match against;
+// `description().name()` is newer and less proven there. Keep `name()` so the
+// listing and the server's device matching use the same reliable string.
+#[allow(deprecated)]
+pub fn output_device_names() -> Vec<String> {
+    use rodio::cpal::traits::{DeviceTrait, HostTrait};
+    match rodio::cpal::default_host().output_devices() {
+        Ok(devices) => devices.filter_map(|device| device.name().ok()).collect(),
+        Err(err) => {
+            warn!("could not enumerate audio output devices: {err}");
+            Vec::new()
+        }
+    }
+}
+
+/// Opens the audio output. With `preferred` set, picks the first output
+/// device whose name contains that string (case-insensitive) — so a user can
+/// name a memorable fragment ("Headphones", "USB") instead of the full ALSA
+/// string — and falls back to the system default with a warning if none
+/// matches (the Pi's default is often HDMI, which is exactly the silent-output
+/// case this selection exists to fix). With `preferred` unset, uses the
+/// system default.
+// `name()` deprecation: see the note on `output_device_names`.
+#[allow(deprecated)]
+fn open_output_device(preferred: Option<&str>) -> Result<MixerDeviceSink> {
+    use rodio::cpal::traits::{DeviceTrait, HostTrait};
+    if let Some(wanted) = preferred {
+        let needle = wanted.to_lowercase();
+        let matched = rodio::cpal::default_host()
+            .output_devices()
+            .ok()
+            .and_then(|mut devices| {
+                devices.find(|device| {
+                    device
+                        .name()
+                        .map(|name| name.to_lowercase().contains(&needle))
+                        .unwrap_or(false)
+                })
+            });
+        match matched {
+            Some(device) => {
+                let name = device.name().unwrap_or_else(|_| "?".to_string());
+                info!(device = %name, "opening selected audio output device");
+                return DeviceSinkBuilder::from_device(device)
+                    .with_context(|| format!("failed to open audio device {name}"))?
+                    .open_stream()
+                    .with_context(|| format!("failed to open a stream on audio device {name}"));
+            }
+            None => warn!(
+                requested = wanted,
+                "no audio output device name matched; using the system default"
+            ),
+        }
+    }
+    DeviceSinkBuilder::open_default_sink().context("failed to open audio output device")
+}
+
 impl PlayerEngine {
     pub fn init(
         tx_engine: Sender<PlayerEngineCommand>,
         tx_player: Sender<PlayerMessage>,
         runtime: Option<tokio::runtime::Handle>,
         spectrum: Arc<SpectrumTap>,
+        device: Option<String>,
     ) -> Result<Self> {
-        let stream =
-            DeviceSinkBuilder::open_default_sink().context("failed to open audio output device")?;
+        let stream = open_output_device(device.as_deref())?;
         let sink = rodio::Player::connect_new(stream.mixer());
         let (runtime, owned_runtime) = match runtime {
             Some(handle) => (handle, None),

cbd-cli/src/lib.rs

@@ -195,6 +195,8 @@ pub enum ServerCommand {
     /// Playback / global operations against a running server.
     #[command(subcommand)]
     Global(GlobalCmd),
+    /// List the audio output devices (to pick `[audio] device`).
+    AudioDevices,
     /// Print a shell completion script.
     Completions(CompletionsArgs),
 }
@@ -249,6 +251,8 @@ pub enum CbdCommand {
     Queue(QueueCmd),
     #[command(subcommand)]
     Global(GlobalCmd),
+    /// List the audio output devices (to pick `[audio] device`).
+    AudioDevices,
     /// Print a shell completion script.
     Completions(CompletionsArgs),
 }

cbd/src/main.rs

@@ -92,6 +92,7 @@ async fn run_command(
     match command {
         CbdCommand::Guard(args) => server_cli::guard(args).await,
         CbdCommand::Scan(args) => server_cli::scan(args).await,
+        CbdCommand::AudioDevices => server_cli::audio_devices(),
         CbdCommand::Auth(args) => {
             let password = args
                 .password

crabidy-server/src/cli.rs

@@ -102,6 +102,51 @@ pub async fn guard(args: GuardArgs) -> Result<(), Box<dyn Error>> {
     Ok(())
 }
 
+/// `audio-devices`: list the available audio output devices so the user can
+/// choose one for `[audio] device` in `crabidy-server.toml`. Marks the device
+/// the current config selects, using the same case-insensitive substring match
+/// the server applies at startup. Fixes the common Raspberry Pi case where the
+/// default device is HDMI and audio plays but is silent on the jack/DAC.
+pub fn audio_devices() -> Result<(), Box<dyn Error>> {
+    let dir = config_dir().ok();
+    let configured = dir
+        .as_deref()
+        .and_then(|dir| ServerSettings::load(dir).ok())
+        .and_then(|settings| settings.audio.device);
+
+    let names = audio_player::output_device_names();
+    if names.is_empty() {
+        println!("No audio output devices found.");
+        return Ok(());
+    }
+
+    let needle = configured.as_ref().map(|device| device.to_lowercase());
+    println!("Audio output devices (* = selected by the current config):");
+    for name in &names {
+        let selected = needle
+            .as_ref()
+            .is_some_and(|needle| name.to_lowercase().contains(needle));
+        println!("  {}{name}", if selected { "* " } else { "  " });
+    }
+
+    match configured {
+        Some(device) => println!("\n[audio] device = \"{device}\""),
+        None => {
+            let path = dir
+                .map(|dir| {
+                    dir.join(crate::settings::SETTINGS_FILE)
+                        .display()
+                        .to_string()
+                })
+                .unwrap_or_else(|| crate::settings::SETTINGS_FILE.to_string());
+            println!(
+                "\nNo [audio] device set (using the system default). To pin one, add to {path}:\n\n[audio]\ndevice = \"Headphones\"   # a name or fragment from the list above"
+            );
+        }
+    }
+    Ok(())
+}
+
 /// The outcome of a `scan` walk, for a concise summary and for tests.
 #[derive(Debug, Default, PartialEq, Eq)]
 pub struct ScanSummary {

crabidy-server/src/lib.rs

@@ -75,6 +75,7 @@ pub async fn serve(
         update_tx.clone(),
         orchestrator.provider_tx.clone(),
         crabidy_store,
+        server_settings.audio.device.clone(),
     );
     // Reload the persisted current queue before anything can observe or
     // mutate state; never starts playback.

crabidy-server/src/main.rs

@@ -41,6 +41,7 @@ async fn run_command(
     match command {
         ServerCommand::Guard(args) => cli::guard(args).await,
         ServerCommand::Scan(args) => cli::scan(args).await,
+        ServerCommand::AudioDevices => cli::audio_devices(),
         ServerCommand::Library(cmd) => {
             cbd_cli::run_remote(&cli::connection(remote), RemoteCmd::Library(cmd)).await
         }

crabidy-server/src/playback.rs

@@ -40,12 +40,13 @@ impl Playback {
         update_tx: tokio::sync::broadcast::Sender<StreamUpdate>,
         provider_tx: flume::Sender<ProviderMessage>,
         store: Option<Arc<CrabidyStore>>,
+        audio_device: Option<String>,
     ) -> Self {
         let (playback_tx, playback_rx) = flume::bounded(64);
         let queue = Mutex::new(QueueManager::new());
         let state = Mutex::new(PlayState::Stopped);
         let (persist_tx, _) = tokio::sync::watch::channel(None);
-        let player = Player::default();
+        let player = Player::new(audio_device);
         Self {
             update_tx,
             provider_tx,
@@ -828,7 +829,7 @@ mod tests {
     fn playback_with(store: Option<Arc<CrabidyStore>>) -> Playback {
         let (update_tx, _) = tokio::sync::broadcast::channel(64);
         let (provider_tx, _provider_rx) = flume::bounded(16);
-        Playback::new(update_tx, provider_tx, store)
+        Playback::new(update_tx, provider_tx, store, None)
     }
 
     fn fill_queue(playback: &Playback, n: usize) {

crabidy-server/src/settings.rs

@@ -34,6 +34,30 @@ pub struct ServerSettings {
     /// Role credentials; absent (or empty) means the server runs open.
     #[serde(default, skip_serializing_if = "AuthSettings::is_default")]
     pub auth: AuthSettings,
+    /// Audio output selection; absent means the system default device.
+    #[serde(default, skip_serializing_if = "AudioSettings::is_default")]
+    pub audio: AudioSettings,
+}
+
+/// Audio output configuration.
+#[derive(Debug, Default, Deserialize, Serialize)]
+#[serde(deny_unknown_fields)]
+pub struct AudioSettings {
+    /// A substring of the output device's name (case-insensitive) to send
+    /// audio to. Absent uses the system default device — which on a Raspberry
+    /// Pi is often HDMI, so audio plays but is silent on the jack/DAC. List
+    /// the available names with `crabidy-server audio-devices`, then set e.g.
+    /// `device = "Headphones"`.
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub device: Option<String>,
+}
+
+impl AudioSettings {
+    /// Whether this is the empty default (no device pinned), so the
+    /// auto-written config omits the `[audio]` table entirely.
+    fn is_default(&self) -> bool {
+        self.device.is_none()
+    }
 }
 
 /// Which providers to mount, resolved from [`ServerSettings::providers`].
@@ -181,6 +205,7 @@ impl ServerSettings {
         let settings = ServerSettings {
             providers: Some(ALL_PROVIDERS.iter().map(|s| s.to_string()).collect()),
             auth: AuthSettings::default(),
+            audio: AudioSettings::default(),
         };
         settings.store(config_dir)
     }