MP3 Support (#14)

src/encoder/mp3.rs

@@ -0,0 +1,72 @@
+use anyhow::anyhow;
+use anyhow::Ok;
+use mp3lame_encoder::Builder;
+use mp3lame_encoder::FlushNoGap;
+use mp3lame_encoder::InterleavedPcm;
+
+use super::execute_with_result;
+use super::EncodedStream;
+use super::Encoder;
+use super::Samples;
+
+pub struct Mp3Encoder;
+
+impl Mp3Encoder {
+    fn build_encoder(
+        &self,
+        sample_rate: u32,
+        channels: u32,
+    ) -> anyhow::Result<mp3lame_encoder::Encoder> {
+        let mut builder = Builder::new().ok_or(anyhow::anyhow!("Failed to create mp3 encoder"))?;
+
+        builder
+            .set_sample_rate(sample_rate)
+            .map_err(|e| anyhow::anyhow!("Failed to set sample rate for mp3 encoder: {}", e))?;
+        builder.set_num_channels(channels as u8).map_err(|e| {
+            anyhow::anyhow!("Failed to set number of channels for mp3 encoder: {}", e)
+        })?;
+        builder
+            .set_brate(mp3lame_encoder::Birtate::Kbps160)
+            .map_err(|e| anyhow::anyhow!("Failed to set bitrate for mp3 encoder: {}", e))?;
+
+        builder
+            .build()
+            .map_err(|e| anyhow::anyhow!("Failed to build mp3 encoder: {}", e))
+    }
+}
+
+#[async_trait::async_trait]
+impl Encoder for Mp3Encoder {
+    async fn encode(&self, samples: Samples) -> anyhow::Result<EncodedStream> {
+        let mut mp3_encoder = self.build_encoder(samples.sample_rate, samples.channels)?;
+
+        let (tx, rx) = tokio::sync::oneshot::channel();
+
+        rayon::spawn(execute_with_result(
+            move || {
+                let samples: Vec<i16> = samples.samples.iter().map(|&x| x as i16).collect();
+                let input = InterleavedPcm(samples.as_slice());
+                let mut mp3_out_buffer = Vec::with_capacity(mp3lame_encoder::max_required_buffer_size(samples.len()));
+                let encoded_size = mp3_encoder
+                    .encode(input, mp3_out_buffer.spare_capacity_mut())
+                    .map_err(|e| anyhow!("Failed to encode mp3: {}", e))?;
+                unsafe {
+                    mp3_out_buffer.set_len(mp3_out_buffer.len().wrapping_add(encoded_size));
+                }
+
+                let encoded_size = mp3_encoder
+                    .flush::<FlushNoGap>(mp3_out_buffer.spare_capacity_mut())
+                    .map_err(|e| anyhow!("Failed to flush mp3 encoder: {}", e))?;
+                unsafe {
+                    mp3_out_buffer.set_len(mp3_out_buffer.len().wrapping_add(encoded_size));
+                }
+                Ok(mp3_out_buffer)
+            },
+            tx,
+        ));
+
+        let mp3_out_buffer = rx.await??;
+
+        Ok(EncodedStream::new(mp3_out_buffer))
+    }
+}