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|
//! ALSA backend implementation.
//!
//! Default backend on Linux and BSD systems.
extern crate alsa;
extern crate libc;
use std::{
cmp,
sync::{
atomic::{AtomicBool, AtomicUsize, Ordering},
Arc,
},
thread::{self, JoinHandle},
time::Duration,
vec::IntoIter as VecIntoIter,
};
use self::alsa::poll::Descriptors;
pub use self::enumerate::Devices;
use crate::{
host::fill_with_equilibrium,
iter::{SupportedInputConfigs, SupportedOutputConfigs},
traits::{DeviceTrait, HostTrait, StreamTrait},
BackendSpecificError, BufferSize, BuildStreamError, ChannelCount, Data,
DefaultStreamConfigError, DeviceDescription, DeviceDescriptionBuilder, DeviceDirection,
DeviceId, DeviceIdError, DeviceNameError, DevicesError, FrameCount, InputCallbackInfo,
OutputCallbackInfo, PauseStreamError, PlayStreamError, SampleFormat, SampleRate, StreamConfig,
StreamError, SupportedBufferSize, SupportedStreamConfig, SupportedStreamConfigRange,
SupportedStreamConfigsError,
};
mod enumerate;
// ALSA Buffer Size Behavior
// =========================
//
// ## ALSA Latency Model
//
// **Hardware vs Software Buffer**: ALSA maintains a software buffer in memory that feeds
// a hardware buffer in the audio device. Audio latency is determined by how much data
// sits in the software buffer before being transferred to hardware.
//
// **Period-Based Transfer**: ALSA transfers data in chunks called "periods". When one
// period worth of data has been consumed by hardware, ALSA triggers a callback to refill
// that period in the software buffer.
//
// ## BufferSize::Fixed Behavior
//
// When `BufferSize::Fixed(x)` is specified, cpal attempts to configure the period size
// to approximately `x` frames to achieve the requested callback size. However, the
// actual callback size may differ from the request:
//
// - ALSA may round the period size to hardware-supported values
// - Different devices have different period size constraints
// - The callback size is not guaranteed to exactly match the request
// - If the requested size cannot be accommodated, ALSA will choose the nearest
// supported configuration
//
// This mirrors the behavior documented in the cpal API where `BufferSize::Fixed(x)`
// requests but does not guarantee a specific callback size.
//
// ## BufferSize::Default Behavior
//
// When `BufferSize::Default` is specified, cpal does NOT set explicit period size or
// period count constraints, allowing the device/driver to choose sensible defaults.
//
// **Why not set defaults?** Different audio systems have different behaviors:
//
// - **Native ALSA hardware**: Typically chooses reasonable defaults (e.g., 512-2048
// frame periods with 2-4 periods)
//
// - **PipeWire-ALSA plugin**: Allocates a large ring buffer (~1M frames at 48kHz) but
// uses small periods (512-1024 frames). Critically, if you request `set_periods(2)`
// without specifying period size, PipeWire calculates period = buffer/2, resulting
// in pathologically large periods (~524K frames = 10 seconds). See issues #1029 and
// #1036.
//
// By not constraining period configuration, PipeWire-ALSA can use its optimized defaults
// (small periods with many-period buffer), while native ALSA hardware uses its own defaults.
//
// **Startup latency**: Regardless of buffer size, cpal uses double-buffering for startup
// (start_threshold = 2 periods), ensuring low latency even with large multi-period ring
// buffers.
const DEFAULT_DEVICE: &str = "default";
// Some ALSA plugins (e.g. alsaequal, certain USB drivers) are not reentrant.
static ALSA_OPEN_MUTEX: std::sync::Mutex<()> = std::sync::Mutex::new(());
// TODO: Not yet defined in rust-lang/libc crate
const LIBC_ENOTSUPP: libc::c_int = 524;
/// The default Linux and BSD host type.
#[derive(Debug, Clone)]
pub struct Host {
inner: Arc<AlsaContext>,
}
impl Host {
pub fn new() -> Result<Self, crate::HostUnavailable> {
let inner = AlsaContext::new().map_err(|_| crate::HostUnavailable)?;
Ok(Host {
inner: Arc::new(inner),
})
}
}
impl HostTrait for Host {
type Devices = Devices;
type Device = Device;
fn is_available() -> bool {
// Assume ALSA is always available on Linux and BSD.
true
}
fn devices(&self) -> Result<Self::Devices, DevicesError> {
self.enumerate_devices()
}
fn device_by_id(&self, id: &crate::DeviceId) -> Option<Self::Device> {
let canonical_id = crate::DeviceId(id.0, canonical_pcm_id(&id.1));
self.devices()
.ok()?
.find(|d| d.id().ok().as_ref() == Some(&canonical_id))
}
fn default_input_device(&self) -> Option<Self::Device> {
Some(Device::default())
}
fn default_output_device(&self) -> Option<Self::Device> {
Some(Device::default())
}
}
/// Global count of active ALSA context instances.
static ALSA_CONTEXT_COUNT: AtomicUsize = AtomicUsize::new(0);
/// ALSA backend context shared between `Host`, `Device`, and `Stream` via `Arc`.
#[derive(Debug)]
pub(super) struct AlsaContext;
impl AlsaContext {
fn new() -> Result<Self, alsa::Error> {
// Initialize global ALSA config cache on first context creation.
if ALSA_CONTEXT_COUNT.fetch_add(1, Ordering::SeqCst) == 0 {
alsa::config::update()?;
}
Ok(Self)
}
}
impl Drop for AlsaContext {
fn drop(&mut self) {
// Free the global ALSA config cache when the last context is dropped.
if ALSA_CONTEXT_COUNT.fetch_sub(1, Ordering::SeqCst) == 1 {
let _ = alsa::config::update_free_global();
}
}
}
impl DeviceTrait for Device {
type SupportedInputConfigs = SupportedInputConfigs;
type SupportedOutputConfigs = SupportedOutputConfigs;
type Stream = Stream;
// ALSA overrides name() to return pcm_id directly instead of from description
fn name(&self) -> Result<String, DeviceNameError> {
Device::name(self)
}
fn description(&self) -> Result<DeviceDescription, DeviceNameError> {
Device::description(self)
}
fn id(&self) -> Result<DeviceId, DeviceIdError> {
Device::id(self)
}
// Override trait defaults to avoid opening devices during enumeration.
//
// ALSA does not guarantee transactional cleanup on failed snd_pcm_open(). Opening plugins like
// alsaequal that fail with EPERM can leak FDs, poisoning the ALSA backend for the process
// lifetime (subsequent device opens fail with EBUSY until process exit).
fn supports_input(&self) -> bool {
matches!(
self.direction,
DeviceDirection::Input | DeviceDirection::Duplex
)
}
fn supports_output(&self) -> bool {
matches!(
self.direction,
DeviceDirection::Output | DeviceDirection::Duplex
)
}
fn supported_input_configs(
&self,
) -> Result<Self::SupportedInputConfigs, SupportedStreamConfigsError> {
Device::supported_input_configs(self)
}
fn supported_output_configs(
&self,
) -> Result<Self::SupportedOutputConfigs, SupportedStreamConfigsError> {
Device::supported_output_configs(self)
}
fn default_input_config(&self) -> Result<SupportedStreamConfig, DefaultStreamConfigError> {
Device::default_input_config(self)
}
fn default_output_config(&self) -> Result<SupportedStreamConfig, DefaultStreamConfigError> {
Device::default_output_config(self)
}
fn build_input_stream_raw<D, E>(
&self,
conf: StreamConfig,
sample_format: SampleFormat,
data_callback: D,
error_callback: E,
timeout: Option<Duration>,
) -> Result<Self::Stream, BuildStreamError>
where
D: FnMut(&Data, &InputCallbackInfo) + Send + 'static,
E: FnMut(StreamError) + Send + 'static,
{
let stream_inner =
self.build_stream_inner(conf, sample_format, alsa::Direction::Capture)?;
let stream = Self::Stream::new_input(
Arc::new(stream_inner),
data_callback,
error_callback,
timeout,
);
Ok(stream)
}
fn build_output_stream_raw<D, E>(
&self,
conf: StreamConfig,
sample_format: SampleFormat,
data_callback: D,
error_callback: E,
timeout: Option<Duration>,
) -> Result<Self::Stream, BuildStreamError>
where
D: FnMut(&mut Data, &OutputCallbackInfo) + Send + 'static,
E: FnMut(StreamError) + Send + 'static,
{
let stream_inner =
self.build_stream_inner(conf, sample_format, alsa::Direction::Playback)?;
let stream = Self::Stream::new_output(
Arc::new(stream_inner),
data_callback,
error_callback,
timeout,
);
Ok(stream)
}
}
#[derive(Debug)]
struct TriggerSender(libc::c_int);
#[derive(Debug)]
struct TriggerReceiver(libc::c_int);
impl TriggerSender {
fn wakeup(&self) {
let buf = 1u64;
loop {
let ret = unsafe { libc::write(self.0, &buf as *const u64 as *const _, 8) };
if ret == 8 {
return;
}
// write() can be interrupted by a signal before writing any bytes; retry.
assert_eq!(ret, -1, "wakeup: unexpected return value {ret}");
if std::io::Error::last_os_error().kind() != std::io::ErrorKind::Interrupted {
panic!("wakeup: {}", std::io::Error::last_os_error());
}
}
}
}
impl TriggerReceiver {
fn clear_pipe(&self) {
let mut out = 0u64;
loop {
let ret = unsafe { libc::read(self.0, &mut out as *mut u64 as *mut _, 8) };
if ret == 8 {
return;
}
// read() can be interrupted by a signal before reading any bytes; retry.
assert_eq!(ret, -1, "clear_pipe: unexpected return value {ret}");
if std::io::Error::last_os_error().kind() != std::io::ErrorKind::Interrupted {
panic!("clear_pipe: {}", std::io::Error::last_os_error());
}
}
}
}
fn trigger() -> (TriggerSender, Arc<TriggerReceiver>) {
let mut fds = [0, 0];
match unsafe { libc::pipe(fds.as_mut_ptr()) } {
0 => (TriggerSender(fds[1]), Arc::new(TriggerReceiver(fds[0]))),
_ => panic!("Could not create pipe"),
}
}
impl Drop for TriggerSender {
fn drop(&mut self) {
unsafe {
libc::close(self.0);
}
}
}
impl Drop for TriggerReceiver {
fn drop(&mut self) {
unsafe {
libc::close(self.0);
}
}
}
#[derive(Clone, Debug)]
pub struct Device {
pcm_id: String,
desc: Option<String>,
direction: DeviceDirection,
_context: Arc<AlsaContext>,
}
impl PartialEq for Device {
fn eq(&self, other: &Self) -> bool {
self.pcm_id == other.pcm_id
}
}
impl Eq for Device {}
impl std::hash::Hash for Device {
fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
self.pcm_id.hash(state);
}
}
impl Device {
fn build_stream_inner(
&self,
conf: StreamConfig,
sample_format: SampleFormat,
stream_type: alsa::Direction,
) -> Result<StreamInner, BuildStreamError> {
// Validate buffer size if Fixed is specified. This is necessary because
// `set_period_size_near()` with `ValueOr::Nearest` will accept ANY value and return the
// "nearest" supported value, which could be wildly different (e.g., requesting 4096 frames
// might return 512 frames if that's "nearest").
if let BufferSize::Fixed(requested_size) = conf.buffer_size {
// Note: We use `default_input_config`/`default_output_config` to get the buffer size
// range. This queries the CURRENT device (`self.pcm_id`), not the default device. The
// buffer size range is the same across all format configurations for a given device
// (see `supported_configs()`).
let supported_config = match stream_type {
alsa::Direction::Capture => self.default_input_config(),
alsa::Direction::Playback => self.default_output_config(),
};
if let Ok(config) = supported_config {
if let SupportedBufferSize::Range { min, max } = config.buffer_size {
if !(min..=max).contains(&requested_size) {
return Err(BuildStreamError::StreamConfigNotSupported);
}
}
}
}
let open_result = {
let _guard = ALSA_OPEN_MUTEX.lock().unwrap_or_else(|e| e.into_inner());
alsa::pcm::PCM::new(&self.pcm_id, stream_type, true).map_err(|e| (e, e.errno()))
};
let handle = match open_result {
Err((_, libc::ENOENT))
| Err((_, libc::EPERM))
| Err((_, libc::ENODEV))
| Err((_, LIBC_ENOTSUPP)) => return Err(BuildStreamError::DeviceNotAvailable),
Err((_, libc::EBUSY)) | Err((_, libc::EAGAIN)) => {
return Err(BuildStreamError::DeviceBusy)
}
Err((_, libc::EINVAL)) => return Err(BuildStreamError::InvalidArgument),
Err((e, _)) => return Err(e.into()),
Ok(handle) => handle,
};
let can_pause = set_hw_params_from_format(&handle, conf, sample_format)?;
let period_samples = set_sw_params_from_format(&handle, conf, stream_type)?;
handle.prepare()?;
let num_descriptors = handle.count();
if num_descriptors == 0 {
let description = "poll descriptor count for stream was 0".to_string();
let err = BackendSpecificError { description };
return Err(err.into());
}
// Check to see if we can retrieve valid timestamps from the device.
// Related: https://bugs.freedesktop.org/show_bug.cgi?id=88503
let ts = handle.status()?.get_htstamp();
let creation_instant = std::time::Instant::now();
let use_hw_timestamps = !(ts.tv_sec == 0 && ts.tv_nsec == 0);
if let alsa::Direction::Capture = stream_type {
handle.start()?;
}
// Pre-compute a period-sized buffer filled with silence values.
let period_frames = period_samples / conf.channels as usize;
let frame_size = sample_format.sample_size() * conf.channels as usize;
let period_bytes = period_frames * frame_size;
let mut silence_template = vec![0u8; period_bytes].into_boxed_slice();
// Only fill buffer for unsigned formats that don't have a zero value for silence.
if sample_format.is_uint() {
fill_with_equilibrium(&mut silence_template, sample_format);
}
let stream_inner = StreamInner {
dropping: AtomicBool::new(false),
channel: handle,
sample_format,
num_descriptors,
conf,
period_samples,
period_frames,
frame_size,
silence_template,
can_pause,
creation_instant,
use_hw_timestamps,
_context: self._context.clone(),
};
Ok(stream_inner)
}
fn name(&self) -> Result<String, DeviceNameError> {
Ok(self.pcm_id.clone())
}
fn description(&self) -> Result<DeviceDescription, DeviceNameError> {
let name = self
.desc
.as_ref()
.and_then(|desc| desc.lines().next())
.unwrap_or(&self.pcm_id)
.to_string();
let mut builder = DeviceDescriptionBuilder::new(name)
.driver(self.pcm_id.clone())
.direction(self.direction);
if let Some(ref desc) = self.desc {
let lines = desc
.lines()
.map(|line| line.trim().to_string())
.filter(|line| !line.is_empty())
.collect();
builder = builder.extended(lines);
}
Ok(builder.build())
}
fn id(&self) -> Result<DeviceId, DeviceIdError> {
Ok(DeviceId(crate::platform::HostId::Alsa, self.pcm_id.clone()))
}
fn supported_configs(
&self,
stream_t: alsa::Direction,
) -> Result<VecIntoIter<SupportedStreamConfigRange>, SupportedStreamConfigsError> {
let open_result = {
let _guard = ALSA_OPEN_MUTEX.lock().unwrap_or_else(|e| e.into_inner());
alsa::pcm::PCM::new(&self.pcm_id, stream_t, true).map_err(|e| (e, e.errno()))
};
let pcm = match open_result {
Err((_, libc::ENOENT))
| Err((_, libc::EPERM))
| Err((_, libc::ENODEV))
| Err((_, LIBC_ENOTSUPP)) => {
return Err(SupportedStreamConfigsError::DeviceNotAvailable)
}
Err((_, libc::EBUSY)) | Err((_, libc::EAGAIN)) => {
return Err(SupportedStreamConfigsError::DeviceBusy)
}
Err((_, libc::EINVAL)) => return Err(SupportedStreamConfigsError::InvalidArgument),
Err((e, _)) => return Err(e.into()),
Ok(pcm) => pcm,
};
let hw_params = alsa::pcm::HwParams::any(&pcm)?;
// Test both LE and BE formats to detect what the hardware actually supports.
// LE is listed first as it's the common case for most audio hardware.
// Hardware reports its supported formats regardless of CPU endianness.
const FORMATS: [(SampleFormat, alsa::pcm::Format); 23] = [
(SampleFormat::I8, alsa::pcm::Format::S8),
(SampleFormat::U8, alsa::pcm::Format::U8),
(SampleFormat::I16, alsa::pcm::Format::S16LE),
(SampleFormat::I16, alsa::pcm::Format::S16BE),
(SampleFormat::U16, alsa::pcm::Format::U16LE),
(SampleFormat::U16, alsa::pcm::Format::U16BE),
(SampleFormat::I24, alsa::pcm::Format::S24LE),
(SampleFormat::I24, alsa::pcm::Format::S24BE),
(SampleFormat::U24, alsa::pcm::Format::U24LE),
(SampleFormat::U24, alsa::pcm::Format::U24BE),
(SampleFormat::I32, alsa::pcm::Format::S32LE),
(SampleFormat::I32, alsa::pcm::Format::S32BE),
(SampleFormat::U32, alsa::pcm::Format::U32LE),
(SampleFormat::U32, alsa::pcm::Format::U32BE),
(SampleFormat::F32, alsa::pcm::Format::FloatLE),
(SampleFormat::F32, alsa::pcm::Format::FloatBE),
(SampleFormat::F64, alsa::pcm::Format::Float64LE),
(SampleFormat::F64, alsa::pcm::Format::Float64BE),
(SampleFormat::DsdU8, alsa::pcm::Format::DSDU8),
(SampleFormat::DsdU16, alsa::pcm::Format::DSDU16LE),
(SampleFormat::DsdU16, alsa::pcm::Format::DSDU16BE),
(SampleFormat::DsdU32, alsa::pcm::Format::DSDU32LE),
(SampleFormat::DsdU32, alsa::pcm::Format::DSDU32BE),
//SND_PCM_FORMAT_IEC958_SUBFRAME_LE,
//SND_PCM_FORMAT_IEC958_SUBFRAME_BE,
//SND_PCM_FORMAT_MU_LAW,
//SND_PCM_FORMAT_A_LAW,
//SND_PCM_FORMAT_IMA_ADPCM,
//SND_PCM_FORMAT_MPEG,
//SND_PCM_FORMAT_GSM,
//SND_PCM_FORMAT_SPECIAL,
//SND_PCM_FORMAT_S24_3LE,
//SND_PCM_FORMAT_S24_3BE,
//SND_PCM_FORMAT_U24_3LE,
//SND_PCM_FORMAT_U24_3BE,
//SND_PCM_FORMAT_S20_3LE,
//SND_PCM_FORMAT_S20_3BE,
//SND_PCM_FORMAT_U20_3LE,
//SND_PCM_FORMAT_U20_3BE,
//SND_PCM_FORMAT_S18_3LE,
//SND_PCM_FORMAT_S18_3BE,
//SND_PCM_FORMAT_U18_3LE,
//SND_PCM_FORMAT_U18_3BE,
];
// Collect supported formats, deduplicating since we test both LE and BE variants.
// If hardware supports both endiannesses (rare), we only report the format once.
let mut supported_formats = Vec::new();
for &(sample_format, alsa_format) in FORMATS.iter() {
if hw_params.test_format(alsa_format).is_ok()
&& !supported_formats.contains(&sample_format)
{
supported_formats.push(sample_format);
}
}
let min_rate = hw_params.get_rate_min()?;
let max_rate = hw_params.get_rate_max()?;
let sample_rates = if min_rate == max_rate || hw_params.test_rate(min_rate + 1).is_ok() {
vec![(min_rate, max_rate)]
} else {
let mut rates = Vec::new();
for &sample_rate in crate::COMMON_SAMPLE_RATES.iter() {
if hw_params.test_rate(sample_rate).is_ok() {
rates.push((sample_rate, sample_rate));
}
}
if rates.is_empty() {
vec![(min_rate, max_rate)]
} else {
rates
}
};
let min_channels = hw_params.get_channels_min()?;
let max_channels = hw_params.get_channels_max()?;
let max_channels = cmp::min(max_channels, 32); // TODO: limiting to 32 channels or too much stuff is returned
let supported_channels = (min_channels..max_channels + 1)
.filter_map(|num| {
if hw_params.test_channels(num).is_ok() {
Some(num as ChannelCount)
} else {
None
}
})
.collect::<Vec<_>>();
let (min_buffer_size, max_buffer_size) = hw_params_buffer_size_min_max(&hw_params);
let buffer_size_range = SupportedBufferSize::Range {
min: min_buffer_size,
max: max_buffer_size,
};
let mut output = Vec::with_capacity(
supported_formats.len() * supported_channels.len() * sample_rates.len(),
);
for &sample_format in supported_formats.iter() {
for &channels in supported_channels.iter() {
for &(min_rate, max_rate) in sample_rates.iter() {
output.push(SupportedStreamConfigRange {
channels,
min_sample_rate: min_rate,
max_sample_rate: max_rate,
buffer_size: buffer_size_range,
sample_format,
});
}
}
}
Ok(output.into_iter())
}
fn supported_input_configs(
&self,
) -> Result<SupportedInputConfigs, SupportedStreamConfigsError> {
self.supported_configs(alsa::Direction::Capture)
}
fn supported_output_configs(
&self,
) -> Result<SupportedOutputConfigs, SupportedStreamConfigsError> {
self.supported_configs(alsa::Direction::Playback)
}
// ALSA does not offer default stream formats, so instead we compare all supported formats by
// the `SupportedStreamConfigRange::cmp_default_heuristics` order and select the greatest.
fn default_config(
&self,
stream_t: alsa::Direction,
) -> Result<SupportedStreamConfig, DefaultStreamConfigError> {
let mut formats: Vec<_> = {
match self.supported_configs(stream_t) {
Err(SupportedStreamConfigsError::DeviceNotAvailable) => {
return Err(DefaultStreamConfigError::DeviceNotAvailable);
}
Err(SupportedStreamConfigsError::DeviceBusy) => {
return Err(DefaultStreamConfigError::DeviceBusy);
}
Err(SupportedStreamConfigsError::InvalidArgument) => {
// this happens sometimes when querying for input and output capabilities, but
// the device supports only one
return Err(DefaultStreamConfigError::StreamTypeNotSupported);
}
Err(SupportedStreamConfigsError::BackendSpecific { err }) => {
return Err(err.into());
}
Ok(fmts) => fmts.collect(),
}
};
formats.sort_by(|a, b| a.cmp_default_heuristics(b));
match formats.into_iter().next_back() {
Some(f) => {
let min_r = f.min_sample_rate;
let max_r = f.max_sample_rate;
let mut format = f.with_max_sample_rate();
const HZ_44100: SampleRate = 44_100;
if min_r <= HZ_44100 && HZ_44100 <= max_r {
format.sample_rate = HZ_44100;
}
Ok(format)
}
None => Err(DefaultStreamConfigError::StreamTypeNotSupported),
}
}
fn default_input_config(&self) -> Result<SupportedStreamConfig, DefaultStreamConfigError> {
self.default_config(alsa::Direction::Capture)
}
fn default_output_config(&self) -> Result<SupportedStreamConfig, DefaultStreamConfigError> {
self.default_config(alsa::Direction::Playback)
}
}
impl Default for Device {
fn default() -> Self {
// "default" is a virtual ALSA device that redirects to the configured default. We cannot
// determine its actual capabilities without opening it, so we return Unknown direction.
Self {
pcm_id: DEFAULT_DEVICE.to_owned(),
desc: Some("Default Audio Device".to_string()),
direction: DeviceDirection::Unknown,
_context: Arc::new(
AlsaContext::new().expect("Failed to initialize ALSA configuration"),
),
}
}
}
#[derive(Debug)]
struct StreamInner {
// Flag used to check when to stop polling, regardless of the state of the stream
// (e.g. broken due to a disconnected device).
dropping: AtomicBool,
// The ALSA channel.
channel: alsa::pcm::PCM,
// When converting between file descriptors and `snd_pcm_t`, this is the number of
// file descriptors that this `snd_pcm_t` uses.
num_descriptors: usize,
// Format of the samples.
sample_format: SampleFormat,
// The configuration used to open this stream.
conf: StreamConfig,
// Cached values for performance in audio callback hot path
period_samples: usize,
period_frames: usize,
frame_size: usize,
silence_template: Box<[u8]>,
#[allow(dead_code)]
// Whether or not the hardware supports pausing the stream.
// TODO: We need an API to expose this. See #197, #284.
can_pause: bool,
// Whether to attempt hardware timestamps via `get_htstamp` / `get_trigger_htstamp`.
//
// When `true`, hardware timestamps are tried first on every callback and we fall back silently
// to `creation_instant` if they are transiently unavailable; e.g. the PulseAudio ALSA plugin
// returns `(0, 0)` for the first several periods after the stream is triggered.
use_hw_timestamps: bool,
// Timestamp origin used by the fallback path. Faster without `Option`.
creation_instant: std::time::Instant,
// Keep ALSA context alive to prevent premature ALSA config cleanup
_context: Arc<AlsaContext>,
}
// Assume that the ALSA library is built with thread safe option.
unsafe impl Sync for StreamInner {}
#[derive(Debug)]
pub struct Stream {
/// The high-priority audio processing thread calling callbacks.
/// Option used for moving out in destructor.
thread: Option<JoinHandle<()>>,
/// Handle to the underlying stream for playback controls.
inner: Arc<StreamInner>,
/// Used to signal to stop processing.
trigger: TriggerSender,
/// Keeps the read end of the self-pipe alive for the lifetime of the Stream, so that
/// `trigger.wakeup()` never writes to a closed pipe, even if the worker exited early.
_rx: Arc<TriggerReceiver>,
}
// Compile-time assertion that Stream is Send and Sync
crate::assert_stream_send!(Stream);
crate::assert_stream_sync!(Stream);
struct StreamWorkerContext {
descriptors: Box<[libc::pollfd]>,
transfer_buffer: Box<[u8]>,
poll_timeout: i32,
}
impl StreamWorkerContext {
fn new(poll_timeout: &Option<Duration>, stream: &StreamInner, rx: &TriggerReceiver) -> Self {
let poll_timeout: i32 = if let Some(d) = poll_timeout {
d.as_millis().try_into().unwrap()
} else {
-1 // Don't timeout, wait forever.
};
// Pre-allocate buffer to exactly one period size with proper equilibrium values.
let transfer_buffer = stream.silence_template.clone();
// Pre-allocate and initialize descriptors vector: 1 for self-pipe + stream.num_descriptors
// for ALSA. The descriptor count is constant for the lifetime of stream parameters, and
// poll() overwrites revents on each call, so we only need to set up fd and events once.
let total_descriptors = 1 + stream.num_descriptors;
let mut descriptors = vec![
libc::pollfd {
fd: 0,
events: 0,
revents: 0
};
total_descriptors
]
.into_boxed_slice();
// Set up self-pipe descriptor at index 0
descriptors[0] = libc::pollfd {
fd: rx.0,
events: libc::POLLIN,
revents: 0,
};
// Set up ALSA descriptors starting at index 1
let filled = stream
.channel
.fill(&mut descriptors[1..])
.expect("Failed to fill ALSA descriptors");
debug_assert_eq!(filled, stream.num_descriptors);
Self {
descriptors,
transfer_buffer,
poll_timeout,
}
}
}
fn input_stream_worker(
rx: Arc<TriggerReceiver>,
stream: &StreamInner,
data_callback: &mut (dyn FnMut(&Data, &InputCallbackInfo) + Send + 'static),
error_callback: &mut (dyn FnMut(StreamError) + Send + 'static),
timeout: Option<Duration>,
) {
boost_current_thread_priority(stream.conf.buffer_size, stream.conf.sample_rate);
let mut ctxt = StreamWorkerContext::new(&timeout, stream, &rx);
loop {
if stream.dropping.load(Ordering::Acquire) {
return;
}
let result = match poll_for_period(&rx, stream, &mut ctxt) {
Ok(Poll::Pending) => continue,
Ok(Poll::Ready {
status,
delay_frames,
}) => process_input(
stream,
&mut ctxt.transfer_buffer,
status,
delay_frames,
data_callback,
),
Err(err) => Err(err),
};
if let Err(err) = result {
match err {
StreamError::BufferUnderrun => {
error_callback(StreamError::BufferUnderrun);
if let Err(err) = stream.channel.prepare() {
error_callback(err.into());
} else if let Err(err) = stream.channel.start() {
error_callback(err.into());
}
}
StreamError::DeviceNotAvailable => {
error_callback(StreamError::DeviceNotAvailable);
return;
}
err => error_callback(err),
}
}
}
}
fn output_stream_worker(
rx: Arc<TriggerReceiver>,
stream: &StreamInner,
data_callback: &mut (dyn FnMut(&mut Data, &OutputCallbackInfo) + Send + 'static),
error_callback: &mut (dyn FnMut(StreamError) + Send + 'static),
timeout: Option<Duration>,
) {
boost_current_thread_priority(stream.conf.buffer_size, stream.conf.sample_rate);
let mut ctxt = StreamWorkerContext::new(&timeout, stream, &rx);
loop {
if stream.dropping.load(Ordering::Acquire) {
return;
}
let result = match poll_for_period(&rx, stream, &mut ctxt) {
Ok(Poll::Pending) => continue,
Ok(Poll::Ready {
status,
delay_frames,
}) => process_output(
stream,
&mut ctxt.transfer_buffer,
status,
delay_frames,
data_callback,
),
Err(err) => Err(err),
};
if let Err(err) = result {
match err {
StreamError::BufferUnderrun => {
error_callback(StreamError::BufferUnderrun);
if let Err(err) = stream.channel.prepare() {
error_callback(err.into());
}
// No need to call start() for output streams after prepare();
// ALSA automatically restarts them when the buffer is refilled
// and the stream is triggered again.
}
StreamError::DeviceNotAvailable => {
error_callback(StreamError::DeviceNotAvailable);
return;
}
err => error_callback(err),
}
}
}
}
#[cfg(feature = "audio_thread_priority")]
fn boost_current_thread_priority(buffer_size: BufferSize, sample_rate: SampleRate) {
use audio_thread_priority::promote_current_thread_to_real_time;
let buffer_size = if let BufferSize::Fixed(buffer_size) = buffer_size {
buffer_size
} else {
// if the buffer size isn't fixed, let audio_thread_priority choose a sensible default value
0
};
if let Err(err) = promote_current_thread_to_real_time(buffer_size, sample_rate) {
eprintln!("Failed to promote audio thread to real-time priority: {err}");
}
}
#[cfg(not(feature = "audio_thread_priority"))]
fn boost_current_thread_priority(_: BufferSize, _: SampleRate) {}
/// Attempt hardware resume from a suspend event (`ESTRPIPE`).
fn try_resume(channel: &alsa::PCM) -> Result<Poll, StreamError> {
match channel.resume() {
// device resumed successfully and will continue running on its own
Ok(()) => Ok(Poll::Pending),
// device is still resuming; poll again until it is ready.
Err(e) if e.errno() == libc::EAGAIN => Ok(Poll::Pending),
// hardware does not support soft resume
Err(e) if e.errno() == libc::ENOSYS => Err(StreamError::BufferUnderrun),
Err(e) => Err(e.into()),
}
}
enum Poll {
Pending,
Ready {
status: alsa::pcm::Status,
delay_frames: usize,
},
}
// This block is shared between both input and output stream worker functions.
fn poll_for_period(
rx: &TriggerReceiver,
stream: &StreamInner,
ctxt: &mut StreamWorkerContext,
) -> Result<Poll, StreamError> {
let StreamWorkerContext {
ref mut descriptors,
ref poll_timeout,
..
} = *ctxt;
let res = alsa::poll::poll(descriptors, *poll_timeout)?;
if res == 0 {
// poll() returned 0: either a timeout or a spurious wakeup. Nothing to do.
return Ok(Poll::Pending);
}
if descriptors[0].revents != 0 {
// Self-pipe fired: the stream is being dropped. Clear the pipe and let the
// worker loop detect the dropping flag on the next iteration.
rx.clear_pipe();
return Ok(Poll::Pending);
}
let revents = stream.channel.revents(&descriptors[1..])?;
// No events: spurious wakeup, poll again.
if revents.is_empty() {
return Ok(Poll::Pending);
}
// POLLHUP/POLLNVAL: the device has been disconnected.
if revents.intersects(alsa::poll::Flags::HUP | alsa::poll::Flags::NVAL) {
return Err(StreamError::DeviceNotAvailable);
}
// POLLERR signals an xrun or suspend; avail() below returns EPIPE/ESTRPIPE accordingly.
// POLLIN/POLLOUT: data is ready, fall through to process it.
let status = stream.channel.status()?;
let avail_frames = match stream.channel.avail() {
// Xrun: recover via prepare() (+ start() for capture, handled by the worker).
Err(err) if err.errno() == libc::EPIPE => return Err(StreamError::BufferUnderrun),
// Suspend: try hardware resume first; fall back to prepare() if unsupported.
Err(err) if err.errno() == libc::ESTRPIPE => return try_resume(&stream.channel),
res => res,
}? as usize;
let delay_frames = match status.get_delay() {
d if d < 0 => 0,
d => d as usize,
};
let available_samples = avail_frames * stream.conf.channels as usize;
// ALSA can have spurious wakeups where poll returns but avail < avail_min.
// This is documented to occur with dmix (timer-driven) and other plugins.
// Verify we have room for at least one full period before processing.
// See: https://bugzilla.kernel.org/show_bug.cgi?id=202499
if available_samples < stream.period_samples {
return Ok(Poll::Pending);
}
Ok(Poll::Ready {
status,
delay_frames,
})
}
// Read input data from ALSA and deliver it to the user.
fn process_input(
stream: &StreamInner,
buffer: &mut [u8],
status: alsa::pcm::Status,
delay_frames: usize,
data_callback: &mut (dyn FnMut(&Data, &InputCallbackInfo) + Send + 'static),
) -> Result<(), StreamError> {
let mut frames_read = 0;
while frames_read < stream.period_frames {
match stream
.channel
.io_bytes()
.readi(&mut buffer[frames_read * stream.frame_size..])
{
Ok(n) => frames_read += n,
Err(err) if err.errno() == libc::EPIPE || err.errno() == libc::ESTRPIPE => {
// EPIPE = xrun, ESTRPIPE = hardware suspend. Both require prepare()+restart;
// attempting resume mid-loop with a partial transfer in the ring buffer is unsafe.
return Err(StreamError::BufferUnderrun);
}
Err(err) if err.errno() == libc::ENODEV => return Err(StreamError::DeviceNotAvailable),
Err(err) => return Err(err.into()),
}
}
let data = buffer.as_mut_ptr() as *mut ();
let data = unsafe { Data::from_parts(data, stream.period_samples, stream.sample_format) };
let callback = if stream.use_hw_timestamps {
stream_timestamp_hardware(&status)
.or_else(|_| stream_timestamp_fallback(stream.creation_instant))
} else {
stream_timestamp_fallback(stream.creation_instant)
}?;
let delay_duration = frames_to_duration(delay_frames, stream.conf.sample_rate);
let capture = callback
.sub(delay_duration)
.ok_or_else(|| BackendSpecificError {
description: "`capture` is earlier than representation supported by `StreamInstant`"
.to_string(),
})?;
let timestamp = crate::InputStreamTimestamp { callback, capture };
let info = crate::InputCallbackInfo { timestamp };
data_callback(&data, &info);
Ok(())
}
// Request data from the user's function and write it via ALSA.
fn process_output(
stream: &StreamInner,
buffer: &mut [u8],
status: alsa::pcm::Status,
delay_frames: usize,
data_callback: &mut (dyn FnMut(&mut Data, &OutputCallbackInfo) + Send + 'static),
) -> Result<(), StreamError> {
// Buffer is always pre-filled with equilibrium, user overwrites what they want
buffer.copy_from_slice(&stream.silence_template);
{
let data = buffer.as_mut_ptr() as *mut ();
let mut data =
unsafe { Data::from_parts(data, stream.period_samples, stream.sample_format) };
let callback = if stream.use_hw_timestamps {
stream_timestamp_hardware(&status)
.or_else(|_| stream_timestamp_fallback(stream.creation_instant))
} else {
stream_timestamp_fallback(stream.creation_instant)
}?;
let delay_duration = frames_to_duration(delay_frames, stream.conf.sample_rate);
let playback = callback
.add(delay_duration)
.ok_or_else(|| BackendSpecificError {
description: "`playback` occurs beyond representation supported by `StreamInstant`"
.to_string(),
})?;
let timestamp = crate::OutputStreamTimestamp { callback, playback };
let info = crate::OutputCallbackInfo { timestamp };
data_callback(&mut data, &info);
}
let mut frames_written = 0;
while frames_written < stream.period_frames {
match stream
.channel
.io_bytes()
.writei(&buffer[frames_written * stream.frame_size..])
{
Ok(n) => frames_written += n,
Err(err) if err.errno() == libc::EPIPE || err.errno() == libc::ESTRPIPE => {
// EPIPE = xrun, ESTRPIPE = hardware suspend. Both require prepare()+restart;
// attempting resume mid-loop with a partial transfer in the ring buffer is unsafe.
return Err(StreamError::BufferUnderrun);
}
Err(err) if err.errno() == libc::ENODEV => return Err(StreamError::DeviceNotAvailable),
Err(err) => return Err(err.into()),
}
}
Ok(())
}
// Use hardware timestamps from ALSA.
//
// This ensures accurate timestamps based on actual hardware timing.
#[inline]
fn stream_timestamp_hardware(
status: &alsa::pcm::Status,
) -> Result<crate::StreamInstant, BackendSpecificError> {
let trigger_ts = status.get_trigger_htstamp();
// trigger_htstamp records when the PCM stream started.
// On the first few callbacks, it might not have been set yet,
// which would yield a huge positive nanos nd cause non-monotonicity
// once it is set. Bail out and let the caller use the fallback.
// See https://github.com/RustAudio/cpal/issues/710
if trigger_ts.tv_sec == 0 && trigger_ts.tv_nsec == 0 {
return Err(BackendSpecificError {
description: "trigger_htstamp not yet set".to_string(),
});
}
let ts = status.get_htstamp();
let nanos = timespec_diff_nanos(ts, trigger_ts);
if nanos < 0 {
let description = format!(
"get_htstamp `{}.{}` was earlier than get_trigger_htstamp `{}.{}`",
ts.tv_sec, ts.tv_nsec, trigger_ts.tv_sec, trigger_ts.tv_nsec
);
return Err(BackendSpecificError { description });
}
Ok(crate::StreamInstant::from_nanos(nanos))
}
// Use elapsed duration since stream creation as fallback when hardware timestamps are unavailable.
//
// This ensures positive values that are compatible with our `StreamInstant` representation.
#[inline]
fn stream_timestamp_fallback(
creation: std::time::Instant,
) -> Result<crate::StreamInstant, BackendSpecificError> {
let now = std::time::Instant::now();
let duration = now.duration_since(creation);
crate::StreamInstant::from_nanos_i128(duration.as_nanos() as i128).ok_or(BackendSpecificError {
description: "stream duration has exceeded `StreamInstant` representation".to_string(),
})
}
// Adapted from `timestamp2ns` here:
// https://fossies.org/linux/alsa-lib/test/audio_time.c
#[inline]
#[allow(clippy::unnecessary_cast)]
fn timespec_to_nanos(ts: libc::timespec) -> i64 {
ts.tv_sec as i64 * 1_000_000_000 + ts.tv_nsec as i64
}
// Adapted from `timediff` here:
// https://fossies.org/linux/alsa-lib/test/audio_time.c
#[inline]
fn timespec_diff_nanos(a: libc::timespec, b: libc::timespec) -> i64 {
timespec_to_nanos(a) - timespec_to_nanos(b)
}
// Convert the given duration in frames at the given sample rate to a `std::time::Duration`.
#[inline]
fn frames_to_duration(frames: usize, rate: crate::SampleRate) -> std::time::Duration {
let secsf = frames as f64 / rate as f64;
let secs = secsf as u64;
let nanos = ((secsf - secs as f64) * 1_000_000_000.0) as u32;
std::time::Duration::new(secs, nanos)
}
impl Stream {
fn new_input<D, E>(
inner: Arc<StreamInner>,
mut data_callback: D,
mut error_callback: E,
timeout: Option<Duration>,
) -> Stream
where
D: FnMut(&Data, &InputCallbackInfo) + Send + 'static,
E: FnMut(StreamError) + Send + 'static,
{
let (tx, rx) = trigger();
let rx_thread = rx.clone();
let stream = inner.clone();
let thread = thread::Builder::new()
.name("cpal_alsa_in".to_owned())
.spawn(move || {
input_stream_worker(
rx_thread,
&stream,
&mut data_callback,
&mut error_callback,
timeout,
);
})
.unwrap();
Self {
thread: Some(thread),
inner,
trigger: tx,
_rx: rx,
}
}
fn new_output<D, E>(
inner: Arc<StreamInner>,
mut data_callback: D,
mut error_callback: E,
timeout: Option<Duration>,
) -> Stream
where
D: FnMut(&mut Data, &OutputCallbackInfo) + Send + 'static,
E: FnMut(StreamError) + Send + 'static,
{
let (tx, rx) = trigger();
let rx_thread = rx.clone();
let stream = inner.clone();
let thread = thread::Builder::new()
.name("cpal_alsa_out".to_owned())
.spawn(move || {
output_stream_worker(
rx_thread,
&stream,
&mut data_callback,
&mut error_callback,
timeout,
);
})
.unwrap();
Self {
thread: Some(thread),
inner,
trigger: tx,
_rx: rx,
}
}
}
impl Drop for Stream {
fn drop(&mut self) {
self.inner.dropping.store(true, Ordering::Release);
self.trigger.wakeup();
if let Some(handle) = self.thread.take() {
let _ = handle.join();
}
}
}
impl StreamTrait for Stream {
fn play(&self) -> Result<(), PlayStreamError> {
self.inner.channel.pause(false).ok();
Ok(())
}
fn pause(&self) -> Result<(), PauseStreamError> {
self.inner.channel.pause(true).ok();
Ok(())
}
fn buffer_size(&self) -> Option<FrameCount> {
Some(self.inner.period_frames as FrameCount)
}
}
// Convert ALSA frames to FrameCount, clamping to valid range.
// ALSA Frames are i64 (64-bit) or i32 (32-bit).
fn clamp_frame_count(buffer_size: alsa::pcm::Frames) -> FrameCount {
buffer_size.max(1).try_into().unwrap_or(FrameCount::MAX)
}
fn hw_params_buffer_size_min_max(hw_params: &alsa::pcm::HwParams) -> (FrameCount, FrameCount) {
let min_buf = hw_params
.get_buffer_size_min()
.map(clamp_frame_count)
.unwrap_or(1);
let max_buf = hw_params
.get_buffer_size_max()
.map(clamp_frame_count)
.unwrap_or(FrameCount::MAX);
(min_buf, max_buf)
}
fn init_hw_params<'a>(
pcm_handle: &'a alsa::pcm::PCM,
config: StreamConfig,
sample_format: SampleFormat,
) -> Result<alsa::pcm::HwParams<'a>, BackendSpecificError> {
let hw_params = alsa::pcm::HwParams::any(pcm_handle)?;
hw_params.set_access(alsa::pcm::Access::RWInterleaved)?;
// Determine which endianness the hardware actually supports for this format.
// We prefer native endian (no conversion needed) but fall back to the opposite
// endian if that's all the hardware supports (e.g., LE USB DAC on BE system).
let alsa_format = sample_format_to_alsa_format(&hw_params, sample_format)?;
hw_params.set_format(alsa_format)?;
hw_params.set_rate(config.sample_rate, alsa::ValueOr::Nearest)?;
hw_params.set_channels(config.channels as u32)?;
Ok(hw_params)
}
/// Convert SampleFormat to the appropriate alsa::pcm::Format based on what the hardware supports.
/// Prefers native endian, falls back to non-native if that's all the hardware supports.
fn sample_format_to_alsa_format(
hw_params: &alsa::pcm::HwParams,
sample_format: SampleFormat,
) -> Result<alsa::pcm::Format, BackendSpecificError> {
use alsa::pcm::Format;
// For each sample format, define (native_endian_format, opposite_endian_format) pairs
let (native, opposite) = match sample_format {
SampleFormat::I8 => return Ok(Format::S8), // No endianness
SampleFormat::U8 => return Ok(Format::U8), // No endianness
#[cfg(target_endian = "little")]
SampleFormat::I16 => (Format::S16LE, Format::S16BE),
#[cfg(target_endian = "big")]
SampleFormat::I16 => (Format::S16BE, Format::S16LE),
#[cfg(target_endian = "little")]
SampleFormat::U16 => (Format::U16LE, Format::U16BE),
#[cfg(target_endian = "big")]
SampleFormat::U16 => (Format::U16BE, Format::U16LE),
#[cfg(target_endian = "little")]
SampleFormat::I24 => (Format::S24LE, Format::S24BE),
#[cfg(target_endian = "big")]
SampleFormat::I24 => (Format::S24BE, Format::S24LE),
#[cfg(target_endian = "little")]
SampleFormat::U24 => (Format::U24LE, Format::U24BE),
#[cfg(target_endian = "big")]
SampleFormat::U24 => (Format::U24BE, Format::U24LE),
#[cfg(target_endian = "little")]
SampleFormat::I32 => (Format::S32LE, Format::S32BE),
#[cfg(target_endian = "big")]
SampleFormat::I32 => (Format::S32BE, Format::S32LE),
#[cfg(target_endian = "little")]
SampleFormat::U32 => (Format::U32LE, Format::U32BE),
#[cfg(target_endian = "big")]
SampleFormat::U32 => (Format::U32BE, Format::U32LE),
#[cfg(target_endian = "little")]
SampleFormat::F32 => (Format::FloatLE, Format::FloatBE),
#[cfg(target_endian = "big")]
SampleFormat::F32 => (Format::FloatBE, Format::FloatLE),
#[cfg(target_endian = "little")]
SampleFormat::F64 => (Format::Float64LE, Format::Float64BE),
#[cfg(target_endian = "big")]
SampleFormat::F64 => (Format::Float64BE, Format::Float64LE),
SampleFormat::DsdU8 => return Ok(Format::DSDU8),
#[cfg(target_endian = "little")]
SampleFormat::DsdU16 => (Format::DSDU16LE, Format::DSDU16BE),
#[cfg(target_endian = "big")]
SampleFormat::DsdU16 => (Format::DSDU16BE, Format::DSDU16LE),
#[cfg(target_endian = "little")]
SampleFormat::DsdU32 => (Format::DSDU32LE, Format::DSDU32BE),
#[cfg(target_endian = "big")]
SampleFormat::DsdU32 => (Format::DSDU32BE, Format::DSDU32LE),
_ => {
return Err(BackendSpecificError {
description: format!("Sample format '{sample_format}' is not supported"),
})
}
};
// Try native endian first (optimal - no conversion needed)
if hw_params.test_format(native).is_ok() {
return Ok(native);
}
// Fall back to opposite endian if hardware only supports that
if hw_params.test_format(opposite).is_ok() {
return Ok(opposite);
}
Err(BackendSpecificError {
description: format!(
"Sample format '{sample_format}' is not supported by hardware in any endianness"
),
})
}
fn set_hw_params_from_format(
pcm_handle: &alsa::pcm::PCM,
config: StreamConfig,
sample_format: SampleFormat,
) -> Result<bool, BackendSpecificError> {
let hw_params = init_hw_params(pcm_handle, config, sample_format)?;
// When BufferSize::Fixed(x) is specified, we configure double-buffering with
// buffer_size = 2x and period_size = x. This provides consistent low-latency
// behavior across different ALSA implementations and hardware.
if let BufferSize::Fixed(buffer_frames) = config.buffer_size {
hw_params.set_buffer_size_near((2 * buffer_frames) as alsa::pcm::Frames)?;
hw_params
.set_period_size_near(buffer_frames as alsa::pcm::Frames, alsa::ValueOr::Nearest)?;
}
// Apply hardware parameters
pcm_handle.hw_params(&hw_params)?;
// For BufferSize::Default, constrain to device's configured period with 2-period buffering.
// PipeWire-ALSA picks a good period size but pairs it with many periods (huge buffer).
// We need to re-initialize hw_params and set BOTH period and buffer to constrain properly.
if config.buffer_size == BufferSize::Default {
if let Ok(period) = hw_params.get_period_size() {
// Re-initialize hw_params to clear previous constraints
let hw_params = init_hw_params(pcm_handle, config, sample_format)?;
// Set both period (to device's chosen value) and buffer (to 2 periods)
hw_params.set_period_size_near(period, alsa::ValueOr::Nearest)?;
hw_params.set_buffer_size_near(2 * period)?;
// Re-apply with new constraints
pcm_handle.hw_params(&hw_params)?;
}
}
Ok(hw_params.can_pause())
}
fn set_sw_params_from_format(
pcm_handle: &alsa::pcm::PCM,
config: StreamConfig,
stream_type: alsa::Direction,
) -> Result<usize, BackendSpecificError> {
let sw_params = pcm_handle.sw_params_current()?;
let period_samples = {
let (buffer, period) = pcm_handle.get_params()?;
if buffer == 0 {
return Err(BackendSpecificError {
description: "initialization resulted in a null buffer".to_string(),
});
}
let start_threshold = match stream_type {
alsa::Direction::Playback => {
// Start playback when 2 periods are filled. This ensures consistent low-latency
// startup regardless of total buffer size (whether 2 or more periods).
2 * period
}
alsa::Direction::Capture => 1,
};
sw_params.set_start_threshold(start_threshold as alsa::pcm::Frames)?;
sw_params.set_avail_min(period as alsa::pcm::Frames)?;
period as usize * config.channels as usize
};
sw_params.set_tstamp_mode(true)?;
sw_params.set_tstamp_type(alsa::pcm::TstampType::MonotonicRaw)?;
// tstamp_type param cannot be changed after the device is opened.
// The default tstamp_type value on most Linux systems is "monotonic",
// let's try to use it if setting the tstamp_type fails.
if pcm_handle.sw_params(&sw_params).is_err() {
sw_params.set_tstamp_type(alsa::pcm::TstampType::Monotonic)?;
pcm_handle.sw_params(&sw_params)?;
}
Ok(period_samples)
}
fn canonical_pcm_id(pcm_id: &str) -> String {
if let Some((prefix, rest)) = pcm_id.split_once(':') {
let (card_str, device_str) = match rest.split_once(',') {
Some((c, d)) => (c.trim(), d.trim()),
None => (rest.trim(), "0"),
};
if !card_str.contains('=') {
if let Ok(device) = device_str.parse::<u32>() {
return format!("{prefix}:CARD={card_str},DEV={device}");
}
}
}
pcm_id.to_owned()
}
impl From<alsa::Error> for BackendSpecificError {
fn from(err: alsa::Error) -> Self {
Self {
description: err.to_string(),
}
}
}
impl From<alsa::Error> for BuildStreamError {
fn from(err: alsa::Error) -> Self {
let err: BackendSpecificError = err.into();
err.into()
}
}
impl From<alsa::Error> for SupportedStreamConfigsError {
fn from(err: alsa::Error) -> Self {
let err: BackendSpecificError = err.into();
err.into()
}
}
impl From<alsa::Error> for PlayStreamError {
fn from(err: alsa::Error) -> Self {
let err: BackendSpecificError = err.into();
err.into()
}
}
impl From<alsa::Error> for PauseStreamError {
fn from(err: alsa::Error) -> Self {
let err: BackendSpecificError = err.into();
err.into()
}
}
impl From<alsa::Error> for StreamError {
fn from(err: alsa::Error) -> Self {
let err: BackendSpecificError = err.into();
err.into()
}
}
|