fix audio playback of 8Khz samples, further cut down on clones/copies

src/audio.rs

@@ -156,18 +156,16 @@ impl AudioSink {
     }
 
     fn process(&mut self, scope: &ProcessScope) -> Result<(), AudioError> {
-        let mut next_outbuf = match self.sample_src.try_recv() {
-            Ok(buf) => buf,
-            Err(tokio::sync::mpsc::error::TryRecvError::Empty) => return Ok(()),
-            Err(err) => return Err(err.into())
-        };
-        self.output_buf.append(&mut next_outbuf);
+        if let Ok(buf) = self.sample_src.try_recv() {
+            self.output_buf.extend(buf);
+        }
 
         if self.port.connected_count()? > 0 && !self.output_buf.is_empty() {
             let outbuf = self.port.as_mut_slice(scope);
-            let mut next_segment: Vec<f32> = self.output_buf.drain(0..(outbuf.len()).min(self.output_buf.len())).collect();
+            let mut next_segment: Vec<f32> = self.output_buf.drain(..(outbuf.len()).min(self.output_buf.len())).collect();
             let underrun = outbuf.len() - next_segment.len();
             if underrun > 0 {
+                log::warn!("Audio stream underrun: {} samples", underrun);
                 next_segment.extend(std::iter::repeat_n(0., underrun));
             }