cpal/examples/feedback.rs

102 lines
4.1 KiB
Rust

//! 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 cpal;
extern crate failure;
const LATENCY_MS: f32 = 150.0;
fn main() -> Result<(), failure::Error> {
let event_loop = cpal::EventLoop::new();
// Default devices.
let input_device = cpal::default_input_device().expect("failed to get default input device");
let output_device = cpal::default_output_device().expect("failed to get default output device");
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 mut format = input_device.default_input_format()?;
format.data_type = cpal::SampleFormat::F32;
// Build streams.
println!("Attempting to build both streams with `{:?}`.", format);
let input_stream_id = event_loop.build_input_stream(&input_device, &format)?;
let output_stream_id = event_loop.build_output_stream(&output_device, &format)?;
println!("Successfully built streams.");
// Create a delay in case the input and output devices aren't synced.
let latency_frames = (LATENCY_MS / 1_000.0) * format.sample_rate.0 as f32;
let latency_samples = latency_frames as usize * format.channels as usize;
// The channel to share samples.
let (tx, rx) = std::sync::mpsc::sync_channel(latency_samples * 2);
// Fill the samples with 0.0 equal to the length of the delay.
for _ in 0..latency_samples {
tx.send(0.0)?;
}
// Play the streams.
println!("Starting the input and output streams with `{}` milliseconds of latency.", LATENCY_MS);
event_loop.play_stream(input_stream_id.clone())?;
event_loop.play_stream(output_stream_id.clone())?;
// Run the event loop on a separate thread.
std::thread::spawn(move || {
event_loop.run(move |id, event| {
let data = match event {
cpal::StreamEvent::Data(data) => data,
cpal::StreamEvent::Close(cpal::StreamCloseCause::Error(err)) => {
eprintln!("stream {:?} closed due to an error: {}", id, err);
return;
}
_ => return,
};
match data {
cpal::StreamData::Input { buffer: cpal::UnknownTypeInputBuffer::F32(buffer) } => {
assert_eq!(id, input_stream_id);
let mut output_fell_behind = false;
for &sample in buffer.iter() {
if tx.try_send(sample).is_err() {
output_fell_behind = true;
}
}
if output_fell_behind {
eprintln!("output stream fell behind: try increasing latency");
}
},
cpal::StreamData::Output { buffer: cpal::UnknownTypeOutputBuffer::F32(mut buffer) } => {
assert_eq!(id, output_stream_id);
let mut input_fell_behind = None;
for sample in buffer.iter_mut() {
*sample = match rx.try_recv() {
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);
}
},
_ => panic!("we're expecting f32 data"),
}
});
});
// Run for 3 seconds before closing.
println!("Playing for 3 seconds... ");
std::thread::sleep(std::time::Duration::from_secs(3));
println!("Done!");
Ok(())
}