snapcast_client/decoder/
opus.rs

1//! Opus decoder using opus-decoder (pure Rust, no C dependencies).
2//!
3//! The snapserver sends a custom "pseudo header":
4//!   4 bytes: ID (0x4F505553 as LE u32)
5//!   4 bytes: sample rate (LE u32)
6//!   2 bytes: bits per sample (LE u16)
7//!   2 bytes: channels (LE u16)
8
9use anyhow::{Result, bail};
10use opus_decoder::OpusDecoder as OpusDec;
11use snapcast_proto::SampleFormat;
12use snapcast_proto::message::codec_header::CodecHeader;
13
14use crate::decoder::Decoder;
15
16const OPUS_ID: u32 = 0x4F50_5553;
17const MAX_FRAME_SIZE: usize = 2880;
18
19/// Parse the Opus pseudo header.
20fn parse_opus_header(payload: &[u8]) -> Result<SampleFormat> {
21    if payload.len() >= 19 && &payload[..8] == b"OpusHead" {
22        let channels = payload[9] as u16;
23        let rate = u32::from_le_bytes(payload[12..16].try_into().unwrap());
24        if channels == 0 || rate == 0 {
25            bail!("invalid OpusHead: rate={rate}, channels={channels}");
26        }
27        return Ok(SampleFormat::new(rate, 16, channels));
28    }
29
30    if payload.len() < 12 {
31        bail!(
32            "Opus header too small ({} bytes, need >= 12)",
33            payload.len()
34        );
35    }
36    let id = u32::from_le_bytes(payload[0..4].try_into().unwrap());
37    if id != OPUS_ID {
38        bail!("not an Opus header (expected 0x{OPUS_ID:08X}, got 0x{id:08X})");
39    }
40    let rate = u32::from_le_bytes(payload[4..8].try_into().unwrap());
41    let bits = u16::from_le_bytes(payload[8..10].try_into().unwrap());
42    let channels = u16::from_le_bytes(payload[10..12].try_into().unwrap());
43    Ok(SampleFormat::new(rate, bits, channels))
44}
45
46/// Opus audio decoder (pure Rust).
47pub struct OpusDecoder {
48    decoder: OpusDec,
49    sample_format: SampleFormat,
50    pcm_buf: Vec<i16>,
51}
52
53impl Decoder for OpusDecoder {
54    fn set_header(&mut self, header: &CodecHeader) -> Result<SampleFormat> {
55        let new = create(header)?;
56        *self = new;
57        Ok(self.sample_format)
58    }
59
60    fn decode(&mut self, data: &mut Vec<u8>) -> Result<bool> {
61        if data.is_empty() {
62            return Ok(false);
63        }
64        tracing::trace!(codec = "opus", input_bytes = data.len(), "decode");
65        let decoded_samples = match self
66            .decoder
67            .decode(data.as_slice(), &mut self.pcm_buf, false)
68        {
69            Ok(n) => n,
70            Err(e) => {
71                tracing::warn!(codec = "opus", error = %e, "decode failed");
72                return Ok(false);
73            }
74        };
75        let total_samples = decoded_samples * self.sample_format.channels() as usize;
76        let mut out = Vec::with_capacity(total_samples * 2);
77        for &s in &self.pcm_buf[..total_samples] {
78            out.extend_from_slice(&s.to_le_bytes());
79        }
80        *data = out;
81        Ok(true)
82    }
83}
84
85/// Create an OpusDecoder from a CodecHeader.
86pub fn create(header: &CodecHeader) -> Result<OpusDecoder> {
87    let sf = parse_opus_header(&header.payload)?;
88    let dec = OpusDec::new(sf.rate(), sf.channels() as usize)
89        .map_err(|e| anyhow::anyhow!("failed to create Opus decoder: {e}"))?;
90    Ok(OpusDecoder {
91        decoder: dec,
92        sample_format: sf,
93        pcm_buf: vec![0i16; MAX_FRAME_SIZE * sf.channels() as usize],
94    })
95}
96#[cfg(test)]
97mod tests {
98    use super::*;
99
100    fn opus_header(rate: u32, bits: u16, channels: u16) -> Vec<u8> {
101        let mut h = Vec::new();
102        h.extend_from_slice(&OPUS_ID.to_le_bytes());
103        h.extend_from_slice(&rate.to_le_bytes());
104        h.extend_from_slice(&bits.to_le_bytes());
105        h.extend_from_slice(&channels.to_le_bytes());
106        h
107    }
108
109    fn opus_head(rate: u32, channels: u8) -> Vec<u8> {
110        let mut h = Vec::new();
111        h.extend_from_slice(b"OpusHead");
112        h.push(1);
113        h.push(channels);
114        h.extend_from_slice(&0u16.to_le_bytes());
115        h.extend_from_slice(&rate.to_le_bytes());
116        h.extend_from_slice(&0u16.to_le_bytes());
117        h.push(0);
118        h
119    }
120
121    #[test]
122    fn parse_header_48000_16_2() {
123        let sf = parse_opus_header(&opus_header(48000, 16, 2)).unwrap();
124        assert_eq!(sf.rate(), 48000);
125        assert_eq!(sf.bits(), 16);
126        assert_eq!(sf.channels(), 2);
127    }
128
129    #[test]
130    fn parse_opus_head_48000_2() {
131        let sf = parse_opus_header(&opus_head(48000, 2)).unwrap();
132        assert_eq!(sf.rate(), 48000);
133        assert_eq!(sf.bits(), 16);
134        assert_eq!(sf.channels(), 2);
135    }
136
137    #[test]
138    fn parse_header_too_small() {
139        assert!(parse_opus_header(&[0; 8]).is_err());
140    }
141
142    #[test]
143    fn parse_header_bad_magic() {
144        let mut h = opus_header(48000, 16, 2);
145        h[0] = 0xFF;
146        assert!(parse_opus_header(&h).is_err());
147    }
148
149    #[test]
150    fn create_decoder_48000_16_2() {
151        let header = CodecHeader {
152            codec: "opus".into(),
153            payload: opus_header(48000, 16, 2),
154        };
155        let dec = create(&header);
156        assert!(dec.is_ok());
157    }
158}
snapcast_client/decoder/opus.rs

snapcast_client/decoder/
opus.rs
