cpal/examples/record_wav.rs

//! Records a WAV file (roughly 3 seconds long) using the default input device and format.
//!
//! The input data is recorded to "$CARGO_MANIFEST_DIR/recorded.wav".

extern crate anyhow;
extern crate cpal;
extern crate hound;

use cpal::traits::{DeviceTrait, HostTrait, StreamTrait};
use std::fs::File;
use std::io::BufWriter;
use std::sync::{Arc, Mutex};

fn main() -> Result<(), anyhow::Error> {
    // Use the default host for working with audio devices.
    let host = cpal::default_host();

    // Setup the default input device and stream with the default input format.
    let device = host
        .default_input_device()
        .expect("Failed to get default input device");
    println!("Default input device: {}", device.name()?);
    let format = device
        .default_input_format()
        .expect("Failed to get default input format");
    println!("Default input format: {:?}", format);
    // The WAV file we're recording to.
    const PATH: &'static str = concat!(env!("CARGO_MANIFEST_DIR"), "/recorded.wav");
    let spec = wav_spec_from_format(&format);
    let writer = hound::WavWriter::create(PATH, spec)?;
    let writer = Arc::new(Mutex::new(Some(writer)));

    // A flag to indicate that recording is in progress.
    println!("Begin recording...");

    // Run the input stream on a separate thread.
    let writer_2 = writer.clone();

    let err_fn = move |err| {
        eprintln!("an error occurred on stream: {}", err);
    };

    let stream = match format.data_type {
        cpal::SampleFormat::F32 => device.build_input_stream(
            &format.shape(),
            move |data| write_input_data::<f32, f32>(data, &writer_2),
            err_fn,
        )?,
        cpal::SampleFormat::I16 => device.build_input_stream(
            &format.shape(),
            move |data| write_input_data::<i16, i16>(data, &writer_2),
            err_fn,
        )?,
        cpal::SampleFormat::U16 => device.build_input_stream(
            &format.shape(),
            move |data| write_input_data::<u16, i16>(data, &writer_2),
            err_fn,
        )?,
    };

    stream.play()?;

    // Let recording go for roughly three seconds.
    std::thread::sleep(std::time::Duration::from_secs(3));
    drop(stream);
    writer.lock().unwrap().take().unwrap().finalize()?;
    println!("Recording {} complete!", PATH);
    Ok(())
}

fn sample_format(format: cpal::SampleFormat) -> hound::SampleFormat {
    match format {
        cpal::SampleFormat::U16 => hound::SampleFormat::Int,
        cpal::SampleFormat::I16 => hound::SampleFormat::Int,
        cpal::SampleFormat::F32 => hound::SampleFormat::Float,
    }
}

fn wav_spec_from_format(format: &cpal::Format) -> hound::WavSpec {
    hound::WavSpec {
        channels: format.channels as _,
        sample_rate: format.sample_rate.0 as _,
        bits_per_sample: (format.data_type.sample_size() * 8) as _,
        sample_format: sample_format(format.data_type),
    }
}

type WavWriterHandle = Arc<Mutex<Option<hound::WavWriter<BufWriter<File>>>>>;

fn write_input_data<T, U>(input: &[T], writer: &WavWriterHandle)
where
    T: cpal::Sample,
    U: cpal::Sample + hound::Sample,
{
    if let Ok(mut guard) = writer.try_lock() {
        if let Some(writer) = guard.as_mut() {
            for &sample in input.iter() {
                let sample: U = cpal::Sample::from(&sample);
                writer.write_sample(sample).ok();
            }
        }
    }
}