snapcast-server 0.5.0

Snapcast server library — embeddable synchronized multiroom audio server
Documentation 
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//! Opus encoder using audiopus.

use anyhow::{Result, bail};
use audiopus::coder::Encoder as OpusEnc;
use audiopus::{Application, Channels, SampleRate};
use snapcast_proto::SampleFormat;

use super::{EncodedChunk, Encoder};
use crate::AudioData;

/// Opus encoder wrapping libopus via audiopus.
pub struct OpusEncoder {
    format: SampleFormat,
    encoder: OpusEnc,
    header: Vec<u8>,
    frame_size: usize,
    warned: bool,
}

impl OpusEncoder {
    /// Create a new Opus encoder. Options: bitrate in kbps (default: 192).
    pub fn new(format: SampleFormat, _options: &str) -> Result<Self> {
        let sample_rate = match format.rate() {
            8000 => SampleRate::Hz8000,
            12000 => SampleRate::Hz12000,
            16000 => SampleRate::Hz16000,
            24000 => SampleRate::Hz24000,
            48000 => SampleRate::Hz48000,
            r => {
                tracing::warn!(codec = "opus", sample_rate = r, "unsupported sample rate");
                bail!("Opus does not support sample rate {r}");
            }
        };
        let channels = match format.channels() {
            1 => Channels::Mono,
            2 => Channels::Stereo,
            c => {
                tracing::warn!(codec = "opus", channels = c, "unsupported channel count");
                bail!("Opus does not support {c} channels");
            }
        };

        let encoder = OpusEnc::new(sample_rate, channels, Application::Audio)?;

        // Build OpusHead identification header
        let mut header = Vec::with_capacity(19);
        header.extend_from_slice(b"OpusHead");
        header.push(1); // version
        header.push(format.channels() as u8);
        header.extend_from_slice(&0u16.to_le_bytes()); // pre-skip
        header.extend_from_slice(&format.rate().to_le_bytes());
        header.extend_from_slice(&0u16.to_le_bytes()); // output gain
        header.push(0); // channel mapping family

        // 20ms frame size
        let frame_size = format.rate() as usize / 50;

        Ok(Self {
            format,
            encoder,
            header,
            frame_size,
            warned: false,
        })
    }
}

impl Encoder for OpusEncoder {
    fn name(&self) -> &str {
        "opus"
    }

    fn header(&self) -> &[u8] {
        &self.header
    }

    fn encode(&mut self, input: &AudioData) -> Result<EncodedChunk> {
        let pcm = match input {
            AudioData::Pcm(data) => std::borrow::Cow::Borrowed(data.as_slice()),
            AudioData::F32(samples) => {
                if !self.warned {
                    self.warned = true;
                    tracing::warn!(
                        codec = "opus",
                        "F32 input requires quantization to 16-bit — consider f32lz4 for lossless path"
                    );
                }
                std::borrow::Cow::Owned(super::f32_to_pcm(samples, 16))
            }
        };

        let channels = self.format.channels() as usize;
        let frame_samples = self.frame_size * channels;
        let frame_bytes = frame_samples * 2; // 16-bit samples
        let total_frames = pcm.len() / (channels * 2);
        tracing::trace!(
            codec = "opus",
            input_bytes = pcm.len(),
            total_frames,
            "encode"
        );

        let mut output = Vec::new();
        let mut encode_buf = [0u8; 4096];

        for chunk in pcm.chunks(frame_bytes) {
            if chunk.len() < frame_bytes {
                break;
            }
            let samples: Vec<i16> = chunk
                .chunks_exact(2)
                .map(|b| i16::from_le_bytes([b[0], b[1]]))
                .collect();

            match self.encoder.encode(&samples, &mut encode_buf) {
                Ok(len) => output.extend_from_slice(&encode_buf[..len]),
                Err(e) => {
                    tracing::warn!(codec = "opus", error = %e, "encode failed");
                    bail!("Opus encode failed: {e}");
                }
            }
        }

        Ok(EncodedChunk { data: output })
    }
}