sample-rate-conversion-feedback.rs

use cpal::traits::{DeviceTrait, EventLoopTrait, HostTrait};
use sample::{ring_buffer, interpolate, signal, Sample, Signal};

fn main() -> Result<(), failure::Error> {
    let host = cpal::default_host();
    let event_loop = host.event_loop();

    // 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");
    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 input_format = input_device.default_input_format()?;
    input_format.data_type = cpal::SampleFormat::I16;
    input_format.channels = 1;

    let mut output_format = output_device.default_output_format()?;
    output_format.data_type = cpal::SampleFormat::I16;
    output_format.channels = 1;

    // Build streams.
    println!("Attempting to build both streams with `{:?}`|`{:?}`.", input_format, output_format);
    let input_stream_id = event_loop.build_input_stream(&input_device, &input_format)?;
    let output_stream_id = event_loop.build_output_stream(&output_device, &output_format)?;
    println!("Successfully built streams.");

    // The channel to share samples.
    let (tx, rx) = std::sync::mpsc::sync_channel(48000);

    // Play the streams.
    println!("Starting the input and output streams.");
    event_loop.play_stream(input_stream_id.clone())?;
    event_loop.play_stream(output_stream_id.clone())?;

    let ring_buffer = ring_buffer::Fixed::from([[0.0]; 100]);
    let sinc = interpolate::Sinc::new(ring_buffer);
    let signal = signal::from_iter(rx.try_iter());
    let mut new_signal = signal.from_hz_to_hz(sinc, input_format.sample_rate.0 as f64, output_format.sample_rate.0 as f64);

    event_loop.run(move |id, result| {
        let data = match result {
            Ok(data) => data,
            Err(err) => {
                eprintln!("an error occurred on stream {:?}: {}", id, err);
                return;
            }
        };

        match data {
            cpal::StreamData::Input { buffer: cpal::UnknownTypeInputBuffer::I16(buffer) } => {
                assert_eq!(id, input_stream_id);
                let mut output_fell_behind = false;
                for &sample in buffer.iter() {
                    let frame = [sample.to_sample::<f64>()];
                    if tx.try_send(frame).is_err() {
                        output_fell_behind = true;
                    }
                }
                if output_fell_behind {
                    eprintln!("output stream fell behind: try increasing latency");
                }
            },
            cpal::StreamData::Output { buffer: cpal::UnknownTypeOutputBuffer::I16(mut buffer) } => {
                assert_eq!(id, output_stream_id);
                let mut input_fell_behind = None;
                for sample in buffer.iter_mut() {
                    *sample = match signal.is_exhausted() {
                        false => new_signal.next()[0].to_sample::<i16>(),
                        true => {
                            input_fell_behind = Some("whoops");
                            new_signal.next()[0].to_sample::<i16>()
                        },
                    };
                }
                if let Some(err) = input_fell_behind {
                    eprintln!("input stream fell behind: {}: try increasing latency", err);
                }
            },
            _ => panic!("we're expecting i16 data"),
        }
    })
}