Add the ability to get backend latency

playback/src/audio_backend/alsa.rs

@@ -456,6 +456,23 @@ impl Sink for AlsaSink {
         Ok(())
     }
 
+    fn get_latency_pcm(&mut self) -> u64 {
+        let buffer_len = self.period_buffer.len();
+
+        self.pcm
+            .as_mut()
+            .and_then(|pcm| {
+                pcm.status().ok().map(|status| {
+                    let delay_frames = status.get_delay();
+
+                    let frames_in_buffer = pcm.bytes_to_frames(buffer_len as isize);
+
+                    (delay_frames + frames_in_buffer) as u64
+                })
+            })
+            .unwrap_or(0)
+    }
+
     sink_as_bytes!();
 }
 

playback/src/audio_backend/mod.rs

@@ -30,6 +30,9 @@ pub trait Sink {
     fn stop(&mut self) -> SinkResult<()> {
         Ok(())
     }
+    fn get_latency_pcm(&mut self) -> u64 {
+        0
+    }
     fn write(&mut self, packet: AudioPacket, converter: &mut Converter) -> SinkResult<()>;
 }
 

playback/src/audio_backend/pulseaudio.rs

@@ -131,6 +131,17 @@ impl Sink for PulseAudioSink {
         Ok(())
     }
 
+    fn get_latency_pcm(&mut self) -> u64 {
+        self.sink
+            .as_mut()
+            .and_then(|sink| {
+                sink.get_latency()
+                    .ok()
+                    .map(|micro_sec| (micro_sec.as_secs_f64() * SAMPLE_RATE as f64).round() as u64)
+            })
+            .unwrap_or(0)
+    }
+
     sink_as_bytes!();
 }