feat: 完善 OTG UAC 音频支持

src/audio/uac/decoder.rs

@@ -0,0 +1,59 @@
+use audiopus::coder::Decoder;
+use audiopus::{Channels, SampleRate};
+
+use crate::error::{AppError, Result};
+
+const CHANNELS: usize = 2;
+const MAX_PACKET_BYTES: usize = 1275;
+const MAX_SAMPLES_PER_CHANNEL: usize = 5760;
+
+pub struct UacOpusDecoder {
+    decoder: Decoder,
+    buffer: Vec<i16>,
+}
+
+impl UacOpusDecoder {
+    pub fn new() -> Result<Self> {
+        let decoder = Decoder::new(SampleRate::Hz48000, Channels::Stereo)
+            .map_err(|error| AppError::AudioError(format!("Opus decoder init failed: {error}")))?;
+        Ok(Self {
+            decoder,
+            buffer: vec![0; MAX_SAMPLES_PER_CHANNEL * CHANNELS],
+        })
+    }
+
+    pub fn decode(&mut self, packet: &[u8]) -> Result<&[i16]> {
+        if packet.is_empty() || packet.len() > MAX_PACKET_BYTES {
+            return Err(AppError::BadRequest(format!(
+                "invalid Opus packet length {}",
+                packet.len()
+            )));
+        }
+
+        let frames = self
+            .decoder
+            .decode(Some(packet), &mut self.buffer, false)
+            .map_err(|error| AppError::AudioError(format!("Opus decode failed: {error}")))?;
+        Ok(&self.buffer[..frames * CHANNELS])
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use audiopus::coder::Encoder;
+    use audiopus::Application;
+
+    #[test]
+    fn decode_preserves_all_stereo_samples() {
+        let encoder =
+            Encoder::new(SampleRate::Hz48000, Channels::Stereo, Application::Audio).unwrap();
+        let pcm = vec![0i16; 960 * CHANNELS];
+        let mut packet = vec![0u8; MAX_PACKET_BYTES];
+        let packet_len = encoder.encode(&pcm, &mut packet).unwrap();
+
+        let mut decoder = UacOpusDecoder::new().unwrap();
+        let decoded = decoder.decode(&packet[..packet_len]).unwrap();
+        assert_eq!(decoded.len(), pcm.len());
+    }
+}