examples/cpal.rs

// Hound -- A wav encoding and decoding library in Rust
// Copyright (C) 2015 Ruud van Asseldonk
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// A copy of the License has been included in the root of the repository.
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// This example shows how to play a wav file using the cpal crate.

extern crate hound;
extern crate cpal;

use std::env;
use std::thread;

fn main() {
    // Make a WavReader that reads the file provided as program argument.
    let fname = env::args().nth(1).expect("no file given");
    let mut reader = hound::WavReader::open(fname).unwrap();
    let spec = reader.spec();

    let endpoint = cpal::get_default_endpoint().unwrap();

    // Pick a playback format supported by the endpoint, which matches the spec
    // of the wav file.
    let format = endpoint.get_supported_formats_list().unwrap()
                         .filter(|f| matches_format(f, &spec))
                         .next()
                         .expect("no supported playback format");

    // A voice in cpal is used for playback.
    let mut voice = cpal::Voice::new(&endpoint, &format).unwrap();

    let mut samples_left = reader.len() as usize;

    let mut append_data = |voice: &mut cpal::Voice| {
        match voice.append_data(samples_left) {
            cpal::UnknownTypeBuffer::I16(mut wrapped_buf) => {
                // We cannot rely on Rust's autoderef here, because we want to
                // call .len() on the buffer, which would cause a deref() of the
                // buffer, not a deref_mut(), and cpal's deref() implementation
                // is to panic.
                let buf: &mut [i16] = &mut *wrapped_buf;
                for (dst, src) in buf.iter_mut().zip(reader.samples::<i16>()) {
                    *dst = src.unwrap();
                }
                samples_left -= buf.len();
            }
            cpal::UnknownTypeBuffer::F32(mut wrapped_buf) => {
                let buf: &mut [f32] = &mut *wrapped_buf;
                for (dst, src) in buf.iter_mut().zip(reader.samples::<f32>()) {
                    *dst = src.unwrap();
                }
                samples_left -= buf.len();
            }
            _ => unreachable!()
        }

        // Loop again if there are samples left.
        samples_left > 0
    };

    // The voice must have some data before playing for the first time.
    let mut has_more = append_data(&mut voice);
    voice.play();

    // Then we keep providing new data until the end of the audio.
    while has_more {
        has_more = append_data(&mut voice);
    }

    // Wait for playback to complete.
    while voice.underflowed() {
        thread::yield_now();
    }
}

fn matches_format(format: &cpal::Format, spec: &hound::WavSpec) -> bool {
    let cpal::SamplesRate(sample_rate) = format.samples_rate;
    if sample_rate != spec.sample_rate {
        return false
    }

    if format.channels.len() != spec.channels as usize {
        return false
    }

    let data_type = match (spec.bits_per_sample, spec.sample_format) {
        (16, hound::SampleFormat::Int) => Some(cpal::SampleFormat::I16),
        (32, hound::SampleFormat::Float) => Some(cpal::SampleFormat::F32),
        _ => None
    };

    if Some(format.data_type) != data_type {
        return false
    }

    // If the sample rate, channel count, and sample format match, then we can
    // play back the file in this format.
    true
}