sang/src/audio_transmitter/mod.rs

use anyhow::{Context, Result};

use cpal::traits::{DeviceTrait, HostTrait, StreamTrait};
use cpal::{FromSample, Sample, SampleFormat};

use tracing::{error, info, trace, warn};

use tokio::sync::mpsc::Receiver;

use crate::task_msg::{PcmFrameMessage, PcmSampleMessage};

pub fn audio_transmitter_main(
    mut rx_for_wire: Receiver<PcmSampleMessage>,
    cpal_output: &cpal::Device,
) -> Result<cpal::Stream> {
    trace!("audio_transmitter started");
    let cpal_output_config = cpal_output.supported_output_configs()
        .context("could not find a suitable audio output configuration. are you root, trying to use a normal user's audio stack? try setting the capability CAP_NET_ADMIN=ep on this binary, and running as the user who is running the audio stack.")?
        .max_by_key(|cfg| {
            if cfg.channels() > 1 { return -999; }
            match cfg.sample_format() {
                SampleFormat::U8 => 10,
                SampleFormat::I8 => 11,
                SampleFormat::U16 => 20,
                SampleFormat::I16 => 21,
                SampleFormat::U32 => 30,
                SampleFormat::I32 => 31,
                SampleFormat::F32 => 40,
                SampleFormat::F64 => 50,
                SampleFormat::U64 => 60,
                SampleFormat::I64 => 61,
                x => { warn!("Backend offered unknown sample format {x}",); -999 }
            }
    }).expect("output device has no supported configurations available")
        .with_max_sample_rate();

    info!(
        "output samples are {} @ {}hz on {} channels",
        &cpal_output_config.sample_format(),
        &cpal_output_config.sample_rate().0,
        &cpal_output_config.channels(),
    );

    let failed_pcm_give = move |e| {
        warn!("dropped some PCM data on output stream?! {}", e);
    };

    let output_stream = match cpal_output_config.sample_format() {
        cpal::SampleFormat::U8 => cpal_output
            .build_output_stream(
                &cpal_output_config.into(),
                move |pcm, _: &_| give_output_pcm::<u8>(pcm, &mut rx_for_wire),
                failed_pcm_give,
                None,
            )
            .context("failed to build output stream")?,
        cpal::SampleFormat::I8 => cpal_output
            .build_output_stream(
                &cpal_output_config.into(),
                move |pcm, _: &_| give_output_pcm::<i8>(pcm, &mut rx_for_wire),
                failed_pcm_give,
                None,
            )
            .context("failed to build output stream")?,
        cpal::SampleFormat::U16 => cpal_output
            .build_output_stream(
                &cpal_output_config.into(),
                move |pcm, _: &_| give_output_pcm::<u16>(pcm, &mut rx_for_wire),
                failed_pcm_give,
                None,
            )
            .context("failed to build output stream")?,
        cpal::SampleFormat::I16 => cpal_output
            .build_output_stream(
                &cpal_output_config.into(),
                move |pcm, _: &_| give_output_pcm::<i16>(pcm, &mut rx_for_wire),
                failed_pcm_give,
                None,
            )
            .context("failed to build output stream")?,
        cpal::SampleFormat::U32 => cpal_output
            .build_output_stream(
                &cpal_output_config.into(),
                move |pcm, _: &_| give_output_pcm::<u32>(pcm, &mut rx_for_wire),
                failed_pcm_give,
                None,
            )
            .context("failed to build output stream")?,
        cpal::SampleFormat::I32 => cpal_output
            .build_output_stream(
                &cpal_output_config.into(),
                move |pcm, _: &_| give_output_pcm::<i32>(pcm, &mut rx_for_wire),
                failed_pcm_give,
                None,
            )
            .context("failed to build output stream")?,
        cpal::SampleFormat::F32 => cpal_output
            .build_output_stream(
                &cpal_output_config.into(),
                move |pcm, _: &_| give_output_pcm::<f32>(pcm, &mut rx_for_wire),
                failed_pcm_give,
                None,
            )
            .context("failed to build output stream")?,
        cpal::SampleFormat::F64 => cpal_output
            .build_output_stream(
                &cpal_output_config.into(),
                move |pcm, _: &_| give_output_pcm::<f64>(pcm, &mut rx_for_wire),
                failed_pcm_give,
                None,
            )
            .context("failed to build output stream")?,
        cpal::SampleFormat::U64 => cpal_output
            .build_output_stream(
                &cpal_output_config.into(),
                move |pcm, _: &_| give_output_pcm::<u64>(pcm, &mut rx_for_wire),
                failed_pcm_give,
                None,
            )
            .context("failed to build output stream")?,
        cpal::SampleFormat::I64 => cpal_output
            .build_output_stream(
                &cpal_output_config.into(),
                move |pcm, _: &_| give_output_pcm::<i64>(pcm, &mut rx_for_wire),
                failed_pcm_give,
                None,
            )
            .context("failed to build output stream")?,
        sample_format => Err(anyhow::Error::msg(format!(
            "unsupported sample format '{}'! please ask developers to add it",
            sample_format
        )))?,
    };

    output_stream
        .play()
        .context("failed to start output audio stream")?;

    Ok(output_stream)
}

fn give_output_pcm<T>(pcm: &mut [T], channel: &mut Receiver<PcmSampleMessage>)
where
    T: Sample + std::fmt::Debug + FromSample<i64> + FromSample<f64>,
{
    trace!("ALSA demands {} samples...", pcm.len());
    for outgoing in pcm.iter_mut() {
        *outgoing = match channel.try_recv() {
            Ok(sample) => sample.to_sample::<T>(),
            Err(_) => {
                warn!("rx_for_wire has no samples for us! carrier dead!");
                warn!("are we able to produce samples quickly enough? CPU OK?");
                T::EQUILIBRIUM
            }
        };
    }
    trace!("gave ALSA the samples");
}