cpal/examples/feedback.rs

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//! Feeds back the input stream directly into the output stream.
//!
//! Assumes that the input and output devices can use the same stream format and that they support
//! the f32 sample format.
//!
//! Uses a delay of `LATENCY_MS` milliseconds in case the default input and output streams are not
//! precisely synchronised.
extern crate anyhow;
extern crate cpal;
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extern crate ringbuf;
use cpal::traits::{DeviceTrait, HostTrait, StreamTrait};
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use ringbuf::RingBuffer;
[WIP] Introduce a `Host` API This is an implementation of the API described at #204. Please see that issue for more details on the motivation. ----- A **Host** provides access to the available audio devices on the system. Some platforms have more than one host available, e.g. wasapi/asio/dsound on windows, alsa/pulse/jack on linux and so on. As a result, some audio devices are only available on certain hosts, while others are only available on other hosts. Every platform supported by CPAL has at least one **DefaultHost** that is guaranteed to be available (alsa, wasapi and coreaudio). Currently, the default hosts are the only hosts supported by CPAL, however this will change as of landing #221 (cc @freesig). These changes should also accommodate support for other hosts such as jack #250 (cc @derekdreery) and pulseaudio (cc @knappador) #259. This introduces a suite of traits allowing for both compile time and runtime dispatch of different hosts and their uniquely associated device and event loop types. A new private **host** module has been added containing the individual host implementations, each in their own submodule gated to the platforms on which they are available. A new **platform** module has been added containing platform-specific items, including a dynamically dispatched host type that allows for easily switching between hosts at runtime. The **ALL_HOSTS** slice contains a **HostId** for each host supported on the current platform. The **available_hosts** function produces a **HostId** for each host that is currently *available* on the platform. The **host_from_id** function allows for initialising a host from its associated ID, failing with a **HostUnavailable** error. The **default_host** function returns the default host and should never fail. Please see the examples for a demonstration of the change in usage. For the most part, things look the same at the surface level, however the role of device enumeration and creating the event loop have been moved from global functions to host methods. The enumerate.rs example has been updated to enumerate all devices for each host, not just the default. **TODO** - [x] Add the new **Host** API - [x] Update examples for the new API. - [x] ALSA host - [ ] WASAPI host - [ ] CoreAudio host - [ ] Emscripten host **Follow-up PR** - [ ] ASIO host #221 cc @ishitatsuyuki more to review for you if you're interested, but it might be easier after #288 lands and this gets rebased.
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const LATENCY_MS: f32 = 150.0;
fn main() -> Result<(), anyhow::Error> {
[WIP] Introduce a `Host` API This is an implementation of the API described at #204. Please see that issue for more details on the motivation. ----- A **Host** provides access to the available audio devices on the system. Some platforms have more than one host available, e.g. wasapi/asio/dsound on windows, alsa/pulse/jack on linux and so on. As a result, some audio devices are only available on certain hosts, while others are only available on other hosts. Every platform supported by CPAL has at least one **DefaultHost** that is guaranteed to be available (alsa, wasapi and coreaudio). Currently, the default hosts are the only hosts supported by CPAL, however this will change as of landing #221 (cc @freesig). These changes should also accommodate support for other hosts such as jack #250 (cc @derekdreery) and pulseaudio (cc @knappador) #259. This introduces a suite of traits allowing for both compile time and runtime dispatch of different hosts and their uniquely associated device and event loop types. A new private **host** module has been added containing the individual host implementations, each in their own submodule gated to the platforms on which they are available. A new **platform** module has been added containing platform-specific items, including a dynamically dispatched host type that allows for easily switching between hosts at runtime. The **ALL_HOSTS** slice contains a **HostId** for each host supported on the current platform. The **available_hosts** function produces a **HostId** for each host that is currently *available* on the platform. The **host_from_id** function allows for initialising a host from its associated ID, failing with a **HostUnavailable** error. The **default_host** function returns the default host and should never fail. Please see the examples for a demonstration of the change in usage. For the most part, things look the same at the surface level, however the role of device enumeration and creating the event loop have been moved from global functions to host methods. The enumerate.rs example has been updated to enumerate all devices for each host, not just the default. **TODO** - [x] Add the new **Host** API - [x] Update examples for the new API. - [x] ALSA host - [ ] WASAPI host - [ ] CoreAudio host - [ ] Emscripten host **Follow-up PR** - [ ] ASIO host #221 cc @ishitatsuyuki more to review for you if you're interested, but it might be easier after #288 lands and this gets rebased.
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let host = cpal::default_host();
// Default devices.
let input_device = host
.default_input_device()
.expect("failed to get default input device");
let output_device = host
.default_output_device()
.expect("failed to get default output device");
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println!("Using default input device: \"{}\"", input_device.name()?);
println!("Using default output device: \"{}\"", output_device.name()?);
// We'll try and use the same format between streams to keep it simple
let shape = input_device.default_input_format()?.shape();
// Create a delay in case the input and output devices aren't synced.
let latency_frames = (LATENCY_MS / 1_000.0) * shape.sample_rate.0 as f32;
let latency_samples = latency_frames as usize * shape.channels as usize;
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// The buffer to share samples
let ring = RingBuffer::new(latency_samples * 2);
let (mut producer, mut consumer) = ring.split();
// Fill the samples with 0.0 equal to the length of the delay.
for _ in 0..latency_samples {
// The ring buffer has twice as much space as necessary to add latency here,
// so this should never fail
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producer.push(0.0).unwrap();
}
let input_data_fn = move |data: &[f32]| {
let mut output_fell_behind = false;
for &sample in data {
if producer.push(sample).is_err() {
output_fell_behind = true;
}
}
if output_fell_behind {
eprintln!("output stream fell behind: try increasing latency");
}
};
let output_data_fn = move |data: &mut [f32]| {
let mut input_fell_behind = None;
for sample in data {
*sample = match consumer.pop() {
Ok(s) => s,
Err(err) => {
input_fell_behind = Some(err);
0.0
}
};
}
if let Some(err) = input_fell_behind {
eprintln!(
"input stream fell behind: {:?}: try increasing latency",
err
);
}
};
// Build streams.
println!(
"Attempting to build both streams with f32 samples and `{:?}`.",
shape
);
let input_stream = input_device.build_input_stream(&shape, input_data_fn, err_fn)?;
let output_stream = output_device.build_output_stream(&shape, output_data_fn, err_fn)?;
println!("Successfully built streams.");
// Play the streams.
println!(
"Starting the input and output streams with `{}` milliseconds of latency.",
LATENCY_MS
);
input_stream.play()?;
output_stream.play()?;
// Run for 3 seconds before closing.
println!("Playing for 3 seconds... ");
std::thread::sleep(std::time::Duration::from_secs(3));
drop(input_stream);
drop(output_stream);
println!("Done!");
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Ok(())
}
fn err_fn(err: cpal::StreamError) {
eprintln!("an error occurred on stream: {}", err);
}