cpal/src/lib.rs

642 lines
23 KiB
Rust

//! # How to use cpal
//!
//! Here are some concepts cpal exposes:
//!
//! - A [**Host**](./trait.Host.html) provides access to the available audio devices on the system.
//! Some platforms have more than one host available, but every platform supported by CPAL has at
//! least one [**DefaultHost**](./trait.Host.html) that is guaranteed to be available.
//! - A [**Device**](./trait.Device.html) is an audio device that may have any number of input and
//! output streams.
//! - A stream is an open flow of audio data. Input streams allow you to receive audio data, output
//! streams allow you to play audio data. You must choose which **Device** will run your stream
//! before you can create one. Often, a default device can be retrieved via the **Host**.
//! - An [**EventLoop**](./trait.EventLoop.html) is a collection of streams being run by one or
//! more **Device**s under a single **Host**. Each stream must belong to an **EventLoop**, and
//! all the streams that belong to an **EventLoop** are managed together.
//!
//! The first step is to initialise the `Host` (for accessing audio devices) and create an
//! `EventLoop`:
//!
//! ```
//! use cpal::traits::HostTrait;
//! let host = cpal::default_host();
//! let event_loop = host.event_loop();
//! ```
//!
//! Then choose a `Device`. The easiest way is to use the default input or output `Device` via the
//! `default_input_device()` or `default_output_device()` functions. Alternatively you can
//! enumerate all the available devices with the `devices()` function. Beware that the
//! `default_*_device()` functions return an `Option` in case no device is available for that
//! stream type on the system.
//!
//! ```no_run
//! # use cpal::traits::HostTrait;
//! # let host = cpal::default_host();
//! let device = host.default_output_device().expect("no output device available");
//! ```
//!
//! Before we can create a stream, we must decide what the format of the audio samples is going to
//! be. You can query all the supported formats with the `supported_input_formats()` and
//! `supported_output_formats()` methods. These produce a list of `SupportedFormat` structs which
//! can later be turned into actual `Format` structs. If you don't want to query the list of
//! formats, you can also build your own `Format` manually, but doing so could lead to an error
//! when building the stream if the format is not supported by the device.
//!
//! > **Note**: the `supported_formats()` method could return an error for example if the device
//! > has been disconnected.
//!
//! ```no_run
//! use cpal::traits::{DeviceTrait, HostTrait};
//! # let host = cpal::default_host();
//! # let device = host.default_output_device().unwrap();
//! let mut supported_formats_range = device.supported_output_formats()
//! .expect("error while querying formats");
//! let format = supported_formats_range.next()
//! .expect("no supported format?!")
//! .with_max_sample_rate();
//! ```
//!
//! Now that we have everything for the stream, we can create it from our event loop:
//!
//! ```no_run
//! use cpal::traits::{DeviceTrait, EventLoopTrait, HostTrait};
//! # let host = cpal::default_host();
//! # let event_loop = host.event_loop();
//! # let device = host.default_output_device().unwrap();
//! # let format = device.supported_output_formats().unwrap().next().unwrap().with_max_sample_rate();
//! let stream_id = event_loop.build_output_stream(&device, &format).unwrap();
//! ```
//!
//! The value returned by `build_output_stream()` is of type `StreamId` and is an identifier that
//! will allow you to control the stream.
//!
//! Now we must start the stream. This is done with the `play_stream()` method on the event loop.
//!
//! ```no_run
//! # use cpal::traits::{EventLoopTrait, HostTrait};
//! # let host = cpal::default_host();
//! # let event_loop = host.event_loop();
//! # let stream_id = unimplemented!();
//! event_loop.play_stream(stream_id).expect("failed to play_stream");
//! ```
//!
//! Now everything is ready! We call `run()` on the `event_loop` to begin processing.
//!
//! ```no_run
//! # use cpal::traits::{EventLoopTrait, HostTrait};
//! # let host = cpal::default_host();
//! # let event_loop = host.event_loop();
//! event_loop.run(move |_stream_id, _stream_result| {
//! // react to stream events and read or write stream data here
//! });
//! ```
//!
//! > **Note**: Calling `run()` will block the thread forever, so it's usually best done in a
//! > separate thread.
//!
//! While `run()` is running, the audio device of the user will from time to time call the callback
//! that you passed to this function. The callback gets passed the stream ID and an instance of type
//! `StreamData` that represents the data that must be read from or written to. The inner
//! `UnknownTypeOutputBuffer` can be one of `I16`, `U16` or `F32` depending on the format that was
//! passed to `build_output_stream`.
//!
//! In this example, we simply fill the given output buffer with zeroes.
//!
//! ```no_run
//! use cpal::{StreamData, UnknownTypeOutputBuffer};
//! use cpal::traits::{EventLoopTrait, HostTrait};
//! # let host = cpal::default_host();
//! # let event_loop = host.event_loop();
//! event_loop.run(move |stream_id, stream_result| {
//! let stream_data = match stream_result {
//! Ok(data) => data,
//! Err(err) => {
//! eprintln!("an error occurred on stream {:?}: {}", stream_id, err);
//! return;
//! }
//! _ => return,
//! };
//!
//! match stream_data {
//! StreamData::Output { buffer: UnknownTypeOutputBuffer::U16(mut buffer) } => {
//! for elem in buffer.iter_mut() {
//! *elem = u16::max_value() / 2;
//! }
//! },
//! StreamData::Output { buffer: UnknownTypeOutputBuffer::I16(mut buffer) } => {
//! for elem in buffer.iter_mut() {
//! *elem = 0;
//! }
//! },
//! StreamData::Output { buffer: UnknownTypeOutputBuffer::F32(mut buffer) } => {
//! for elem in buffer.iter_mut() {
//! *elem = 0.0;
//! }
//! },
//! _ => (),
//! }
//! });
//! ```
#![recursion_limit = "512"]
extern crate failure;
#[cfg(target_os = "windows")]
#[macro_use]
extern crate lazy_static;
// Extern crate declarations with `#[macro_use]` must unfortunately be at crate root.
#[cfg(target_os = "emscripten")]
#[macro_use]
extern crate stdweb;
pub use platform::{
ALL_HOSTS, Device, EventLoop, Host, HostId, StreamId, available_hosts,
default_host, host_from_id,
};
pub use samples_formats::{Sample, SampleFormat};
use failure::Fail;
use std::ops::{Deref, DerefMut};
mod host;
pub mod platform;
mod samples_formats;
pub mod traits;
/// A host's device iterator yielding only *input* devices.
pub type InputDevices<I> = std::iter::Filter<I, fn(&<I as Iterator>::Item) -> bool>;
/// A host's device iterator yielding only *output* devices.
pub type OutputDevices<I> = std::iter::Filter<I, fn(&<I as Iterator>::Item) -> bool>;
/// Number of channels.
pub type ChannelCount = u16;
/// The number of samples processed per second for a single channel of audio.
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
pub struct SampleRate(pub u32);
/// The format of an input or output audio stream.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Format {
pub channels: ChannelCount,
pub sample_rate: SampleRate,
pub data_type: SampleFormat,
}
/// Describes a range of supported stream formats.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct SupportedFormat {
pub channels: ChannelCount,
/// Minimum value for the samples rate of the supported formats.
pub min_sample_rate: SampleRate,
/// Maximum value for the samples rate of the supported formats.
pub max_sample_rate: SampleRate,
/// Type of data expected by the device.
pub data_type: SampleFormat,
}
/// Stream data passed to the `EventLoop::run` callback.
pub enum StreamData<'a> {
Input {
buffer: UnknownTypeInputBuffer<'a>,
},
Output {
buffer: UnknownTypeOutputBuffer<'a>,
},
}
/// Stream data passed to the `EventLoop::run` callback, or an error in the case that the device
/// was invalidated or some backend-specific error occurred.
pub type StreamDataResult<'a> = Result<StreamData<'a>, StreamError>;
/// Represents a buffer containing audio data that may be read.
///
/// This struct implements the `Deref` trait targeting `[T]`. Therefore this buffer can be read the
/// same way as reading from a `Vec` or any other kind of Rust array.
// TODO: explain audio stuff in general
// TODO: remove the wrapper and just use slices in next major version
pub struct InputBuffer<'a, T: 'a>
where
T: Sample,
{
buffer: &'a [T],
}
/// Represents a buffer that must be filled with audio data. The buffer in unfilled state may
/// contain garbage values.
///
/// This struct implements the `Deref` and `DerefMut` traits to `[T]`. Therefore writing to this
/// buffer is done in the same way as writing to a `Vec` or any other kind of Rust array.
// TODO: explain audio stuff in general
// TODO: remove the wrapper and just use slices
#[must_use]
pub struct OutputBuffer<'a, T: 'a>
where
T: Sample,
{
buffer: &'a mut [T],
}
/// This is the struct that is provided to you by cpal when you want to read samples from a buffer.
///
/// Since the type of data is only known at runtime, you have to read the right buffer.
pub enum UnknownTypeInputBuffer<'a> {
/// Samples whose format is `u16`.
U16(InputBuffer<'a, u16>),
/// Samples whose format is `i16`.
I16(InputBuffer<'a, i16>),
/// Samples whose format is `f32`.
F32(InputBuffer<'a, f32>),
}
/// This is the struct that is provided to you by cpal when you want to write samples to a buffer.
///
/// Since the type of data is only known at runtime, you have to fill the right buffer.
pub enum UnknownTypeOutputBuffer<'a> {
/// Samples whose format is `u16`.
U16(OutputBuffer<'a, u16>),
/// Samples whose format is `i16`.
I16(OutputBuffer<'a, i16>),
/// Samples whose format is `f32`.
F32(OutputBuffer<'a, f32>),
}
/// The requested host, although supported on this platform, is unavailable.
#[derive(Clone, Debug, Fail)]
#[fail(display = "the requested host is unavailable")]
pub struct HostUnavailable;
/// Some error has occurred that is specific to the backend from which it was produced.
///
/// This error is often used as a catch-all in cases where:
///
/// - It is unclear exactly what error might be produced by the backend API.
/// - It does not make sense to add a variant to the enclosing error type.
/// - No error was expected to occur at all, but we return an error to avoid the possibility of a
/// `panic!` caused by some unforseen or unknown reason.
///
/// **Note:** If you notice a `BackendSpecificError` that you believe could be better handled in a
/// cross-platform manner, please create an issue or submit a pull request with a patch that adds
/// the necessary error variant to the appropriate error enum.
#[derive(Clone, Debug, Fail)]
#[fail(display = "A backend-specific error has occurred: {}", description)]
pub struct BackendSpecificError {
pub description: String
}
/// An error that might occur while attempting to enumerate the available devices on a system.
#[derive(Debug, Fail)]
pub enum DevicesError {
/// See the `BackendSpecificError` docs for more information about this error variant.
#[fail(display = "{}", err)]
BackendSpecific {
#[fail(cause)]
err: BackendSpecificError,
}
}
/// An error that may occur while attempting to retrieve a device name.
#[derive(Debug, Fail)]
pub enum DeviceNameError {
/// See the `BackendSpecificError` docs for more information about this error variant.
#[fail(display = "{}", err)]
BackendSpecific {
#[fail(cause)]
err: BackendSpecificError,
}
}
/// Error that can happen when enumerating the list of supported formats.
#[derive(Debug, Fail)]
pub enum SupportedFormatsError {
/// The device no longer exists. This can happen if the device is disconnected while the
/// program is running.
#[fail(display = "The requested device is no longer available. For example, it has been unplugged.")]
DeviceNotAvailable,
/// We called something the C-Layer did not understand
#[fail(display = "Invalid argument passed to the backend. For example, this happens when trying to read capture capabilities when the device does not support it.")]
InvalidArgument,
/// See the `BackendSpecificError` docs for more information about this error variant.
#[fail(display = "{}", err)]
BackendSpecific {
#[fail(cause)]
err: BackendSpecificError,
}
}
/// May occur when attempting to request the default input or output stream format from a `Device`.
#[derive(Debug, Fail)]
pub enum DefaultFormatError {
/// The device no longer exists. This can happen if the device is disconnected while the
/// program is running.
#[fail(display = "The requested device is no longer available. For example, it has been unplugged.")]
DeviceNotAvailable,
/// Returned if e.g. the default input format was requested on an output-only audio device.
#[fail(display = "The requested stream type is not supported by the device.")]
StreamTypeNotSupported,
/// See the `BackendSpecificError` docs for more information about this error variant.
#[fail(display = "{}", err)]
BackendSpecific {
#[fail(cause)]
err: BackendSpecificError,
}
}
/// Error that can happen when creating a `Stream`.
#[derive(Debug, Fail)]
pub enum BuildStreamError {
/// The device no longer exists. This can happen if the device is disconnected while the
/// program is running.
#[fail(display = "The requested device is no longer available. For example, it has been unplugged.")]
DeviceNotAvailable,
/// The required format is not supported.
#[fail(display = "The requested stream format is not supported by the device.")]
FormatNotSupported,
/// We called something the C-Layer did not understand
///
/// On ALSA device functions called with a feature they do not support will yield this. E.g.
/// Trying to use capture capabilities on an output only format yields this.
#[fail(display = "The requested device does not support this capability (invalid argument)")]
InvalidArgument,
/// Occurs if adding a new Stream ID would cause an integer overflow.
#[fail(display = "Adding a new stream ID would cause an overflow")]
StreamIdOverflow,
/// See the `BackendSpecificError` docs for more information about this error variant.
#[fail(display = "{}", err)]
BackendSpecific {
#[fail(cause)]
err: BackendSpecificError,
}
}
/// Errors that might occur when calling `play_stream`.
///
/// As of writing this, only macOS may immediately return an error while calling this method. This
/// is because both the alsa and wasapi backends only enqueue these commands and do not process
/// them immediately.
#[derive(Debug, Fail)]
pub enum PlayStreamError {
/// The device associated with the stream is no longer available.
#[fail(display = "the device associated with the stream is no longer available")]
DeviceNotAvailable,
/// See the `BackendSpecificError` docs for more information about this error variant.
#[fail(display = "{}", err)]
BackendSpecific {
#[fail(cause)]
err: BackendSpecificError,
}
}
/// Errors that might occur when calling `pause_stream`.
///
/// As of writing this, only macOS may immediately return an error while calling this method. This
/// is because both the alsa and wasapi backends only enqueue these commands and do not process
/// them immediately.
#[derive(Debug, Fail)]
pub enum PauseStreamError {
/// The device associated with the stream is no longer available.
#[fail(display = "the device associated with the stream is no longer available")]
DeviceNotAvailable,
/// See the `BackendSpecificError` docs for more information about this error variant.
#[fail(display = "{}", err)]
BackendSpecific {
#[fail(cause)]
err: BackendSpecificError,
}
}
/// Errors that might occur while a stream is running.
#[derive(Debug, Fail)]
pub enum StreamError {
/// The device no longer exists. This can happen if the device is disconnected while the
/// program is running.
#[fail(display = "The requested device is no longer available. For example, it has been unplugged.")]
DeviceNotAvailable,
/// See the `BackendSpecificError` docs for more information about this error variant.
#[fail(display = "{}", err)]
BackendSpecific {
#[fail(cause)]
err: BackendSpecificError,
}
}
impl SupportedFormat {
/// Turns this `SupportedFormat` into a `Format` corresponding to the maximum samples rate.
#[inline]
pub fn with_max_sample_rate(self) -> Format {
Format {
channels: self.channels,
sample_rate: self.max_sample_rate,
data_type: self.data_type,
}
}
/// A comparison function which compares two `SupportedFormat`s in terms of their priority of
/// use as a default stream format.
///
/// Some backends do not provide a default stream format for their audio devices. In these
/// cases, CPAL attempts to decide on a reasonable default format for the user. To do this we
/// use the "greatest" of all supported stream formats when compared with this method.
///
/// Formats are prioritised by the following heuristics:
///
/// **Channels**:
///
/// - Stereo
/// - Mono
/// - Max available channels
///
/// **Sample format**:
/// - f32
/// - i16
/// - u16
///
/// **Sample rate**:
///
/// - 44100 (cd quality)
/// - Max sample rate
pub fn cmp_default_heuristics(&self, other: &Self) -> std::cmp::Ordering {
use std::cmp::Ordering::Equal;
use SampleFormat::{F32, I16, U16};
let cmp_stereo = (self.channels == 2).cmp(&(other.channels == 2));
if cmp_stereo != Equal {
return cmp_stereo;
}
let cmp_mono = (self.channels == 1).cmp(&(other.channels == 1));
if cmp_mono != Equal {
return cmp_mono;
}
let cmp_channels = self.channels.cmp(&other.channels);
if cmp_channels != Equal {
return cmp_channels;
}
let cmp_f32 = (self.data_type == F32).cmp(&(other.data_type == F32));
if cmp_f32 != Equal {
return cmp_f32;
}
let cmp_i16 = (self.data_type == I16).cmp(&(other.data_type == I16));
if cmp_i16 != Equal {
return cmp_i16;
}
let cmp_u16 = (self.data_type == U16).cmp(&(other.data_type == U16));
if cmp_u16 != Equal {
return cmp_u16;
}
const HZ_44100: SampleRate = SampleRate(44_100);
let r44100_in_self = self.min_sample_rate <= HZ_44100
&& HZ_44100 <= self.max_sample_rate;
let r44100_in_other = other.min_sample_rate <= HZ_44100
&& HZ_44100 <= other.max_sample_rate;
let cmp_r44100 = r44100_in_self.cmp(&r44100_in_other);
if cmp_r44100 != Equal {
return cmp_r44100;
}
self.max_sample_rate.cmp(&other.max_sample_rate)
}
}
impl<'a, T> Deref for InputBuffer<'a, T>
where T: Sample
{
type Target = [T];
#[inline]
fn deref(&self) -> &[T] {
self.buffer
}
}
impl<'a, T> Deref for OutputBuffer<'a, T>
where T: Sample
{
type Target = [T];
#[inline]
fn deref(&self) -> &[T] {
self.buffer
}
}
impl<'a, T> DerefMut for OutputBuffer<'a, T>
where T: Sample
{
#[inline]
fn deref_mut(&mut self) -> &mut [T] {
self.buffer
}
}
impl<'a> UnknownTypeInputBuffer<'a> {
/// Returns the length of the buffer in number of samples.
#[inline]
pub fn len(&self) -> usize {
match self {
&UnknownTypeInputBuffer::U16(ref buf) => buf.len(),
&UnknownTypeInputBuffer::I16(ref buf) => buf.len(),
&UnknownTypeInputBuffer::F32(ref buf) => buf.len(),
}
}
}
impl<'a> UnknownTypeOutputBuffer<'a> {
/// Returns the length of the buffer in number of samples.
#[inline]
pub fn len(&self) -> usize {
match self {
&UnknownTypeOutputBuffer::U16(ref buf) => buf.len(),
&UnknownTypeOutputBuffer::I16(ref buf) => buf.len(),
&UnknownTypeOutputBuffer::F32(ref buf) => buf.len(),
}
}
}
impl From<Format> for SupportedFormat {
#[inline]
fn from(format: Format) -> SupportedFormat {
SupportedFormat {
channels: format.channels,
min_sample_rate: format.sample_rate,
max_sample_rate: format.sample_rate,
data_type: format.data_type,
}
}
}
impl From<BackendSpecificError> for DevicesError {
fn from(err: BackendSpecificError) -> Self {
DevicesError::BackendSpecific { err }
}
}
impl From<BackendSpecificError> for DeviceNameError {
fn from(err: BackendSpecificError) -> Self {
DeviceNameError::BackendSpecific { err }
}
}
impl From<BackendSpecificError> for SupportedFormatsError {
fn from(err: BackendSpecificError) -> Self {
SupportedFormatsError::BackendSpecific { err }
}
}
impl From<BackendSpecificError> for DefaultFormatError {
fn from(err: BackendSpecificError) -> Self {
DefaultFormatError::BackendSpecific { err }
}
}
impl From<BackendSpecificError> for BuildStreamError {
fn from(err: BackendSpecificError) -> Self {
BuildStreamError::BackendSpecific { err }
}
}
impl From<BackendSpecificError> for PlayStreamError {
fn from(err: BackendSpecificError) -> Self {
PlayStreamError::BackendSpecific { err }
}
}
impl From<BackendSpecificError> for PauseStreamError {
fn from(err: BackendSpecificError) -> Self {
PauseStreamError::BackendSpecific { err }
}
}
impl From<BackendSpecificError> for StreamError {
fn from(err: BackendSpecificError) -> Self {
StreamError::BackendSpecific { err }
}
}
// If a backend does not provide an API for retrieving supported formats, we query it with a bunch
// of commonly used rates. This is always the case for wasapi and is sometimes the case for alsa.
//
// If a rate you desire is missing from this list, feel free to add it!
#[cfg(target_os = "windows")]
const COMMON_SAMPLE_RATES: &'static [SampleRate] = &[
SampleRate(5512),
SampleRate(8000),
SampleRate(11025),
SampleRate(16000),
SampleRate(22050),
SampleRate(32000),
SampleRate(44100),
SampleRate(48000),
SampleRate(64000),
SampleRate(88200),
SampleRate(96000),
SampleRate(176400),
SampleRate(192000),
];