Make silence more efficient

src/queue.rs

@@ -206,7 +206,7 @@ where
             if next.len() == 0 {
                 if self.input.keep_alive_if_empty.load(Ordering::Acquire) {
                     // Play a short silence in order to avoid spinlocking.
-                    let silence = Zero::<S>::new(1, 44000); // TODO: meh
+                    let silence = Zero::<S>::new(1, 44100); // TODO: meh
                     (
                         Box::new(silence.take_duration(Duration::from_millis(10))) as Box<_>,
                         None,

src/source/take.rs

@@ -4,8 +4,14 @@ use Sample;
 use Source;
 
 /// Internal function that builds a `TakeDuration` object.
-pub fn take_duration<I>(input: I, duration: Duration) -> TakeDuration<I> {
+pub fn take_duration<I>(input: I, duration: Duration) -> TakeDuration<I>
+where
+    I: Source,
+    I::Item: Sample,
+{
     TakeDuration {
+        current_frame_len: input.current_frame_len(),
+        duration_per_sample: TakeDuration::get_duration_per_sample(&input),
         input: input,
         remaining_duration: duration,
         requested_duration: duration,
@@ -35,6 +41,8 @@ impl DurationFilter
     }
 }
 
+const NANOS_PER_SEC: u64 = 1_000_000_000;
+
 /// A source that repeats the given source.
 #[derive(Clone, Debug)]
 pub struct TakeDuration<I> {
@@ -42,6 +50,10 @@ pub struct TakeDuration<I> {
     remaining_duration: Duration,
     requested_duration: Duration,
     filter: Option<DurationFilter>,
+    // Remaining samples in current frame.
+    current_frame_len: Option<usize>,
+    // Only updated when the current frame len is exausted.
+    duration_per_sample: Duration,
 }
 
 impl<I> TakeDuration<I>
@@ -51,8 +63,8 @@ where
 {
     /// Returns the duration elapsed for each sample extracted.
     #[inline]
-    fn get_duration_per_sample(&self) -> Duration {
-        let ns = 1000000000 / (self.input.sample_rate() as u64 * self.channels() as u64);
+    fn get_duration_per_sample(input: &I) -> Duration {
+        let ns = NANOS_PER_SEC / input.sample_rate() as u64 * input.channels() as u64;
         // \|/ the maximum value of `ns` is one billion, so this can't fail
         Duration::new(0, ns as u32)
     }
@@ -92,9 +104,17 @@ where
     type Item = <I as Iterator>::Item;
 
     fn next(&mut self) -> Option<<I as Iterator>::Item> {
-        let duration_per_sample = self.get_duration_per_sample();
+        if let Some(frame_len) = self.current_frame_len.take() {
+            if frame_len > 0 {
+                self.current_frame_len = Some(frame_len - 1);
+            } else {
+                self.current_frame_len = self.input.current_frame_len();
+                // Sample rate might have changed
+                self.duration_per_sample = Self::get_duration_per_sample(&self.input);
+            }
+        }
 
-        if self.remaining_duration <= duration_per_sample {
+        if self.remaining_duration <= self.duration_per_sample {
             None
         } else {
             if let Some(sample) = self.input.next() {
@@ -102,7 +122,9 @@ where
                     Some(filter) => filter.apply(sample, &self),
                     None => sample,
                 };
-                self.remaining_duration = self.remaining_duration - duration_per_sample;
+
+                self.remaining_duration = self.remaining_duration - self.duration_per_sample;
+                
                 Some(sample)
             } else {
                 None
@@ -120,20 +142,15 @@ where
 {
     #[inline]
     fn current_frame_len(&self) -> Option<usize> {
-        let remaining_nanosecs = self.remaining_duration.as_secs() * 1000000000
+        let remaining_nanos = self.remaining_duration.as_secs() * NANOS_PER_SEC
             + self.remaining_duration.subsec_nanos() as u64;
-        let remaining_samples = remaining_nanosecs * self.input.sample_rate() as u64
-            * self.channels() as u64 / 1000000000;
+        let nanos_per_sample = self.duration_per_sample.as_secs() * NANOS_PER_SEC
+            + self.duration_per_sample.subsec_nanos() as u64;
+        let remaining_samples = (remaining_nanos / nanos_per_sample) as usize;
 
-        if let Some(value) = self.input.current_frame_len() {
-            if (value as u64) < remaining_samples {
-                Some(value)
-            } else {
-                Some(remaining_samples as usize)
-            }
-        } else {
-            Some(remaining_samples as usize)
-        }
+        self.input.current_frame_len()
+            .filter(|value| *value < remaining_samples)
+            .or(Some(remaining_samples))
     }
 
     #[inline]