SourcesQueueOutput can peek metadata from next source

src/buffer.rs

@@ -73,7 +73,7 @@ impl SamplesBuffer {
 impl Source for SamplesBuffer {
     #[inline]
     fn current_span_len(&self) -> Option<usize> {
-        None
+        Some(self.data.len() - self.pos)
     }
 
     #[inline]
@@ -126,7 +126,7 @@ impl Iterator for SamplesBuffer {
 
     #[inline]
     fn size_hint(&self) -> (usize, Option<usize>) {
-        (self.data.len(), Some(self.data.len()))
+        (self.data.len() - self.pos, Some(self.data.len() - self.pos))
     }
 }
 

src/queue.rs

@@ -113,6 +113,8 @@ pub struct SourcesQueueOutput {
 }
 
 const THRESHOLD: usize = 512;
+const SILENCE_SAMPLE_RATE: SampleRate = nz!(44100);
+const SILENCE_CHANNELS: ChannelCount = nz!(1);
 
 impl Source for SourcesQueueOutput {
     #[inline]
@@ -154,12 +156,28 @@ impl Source for SourcesQueueOutput {
 
     #[inline]
     fn channels(&self) -> ChannelCount {
-        self.current.channels()
+        // current_span_len() should never return 0 unless the source is empty, so this is a cheeky hint
+        if self.current.current_span_len() != Some(0) {
+            self.current.channels()
+        } else if let Some((next, _)) = self.input.next_sounds.lock().unwrap().first() {
+            next.channels()
+        } else {
+            // If keep_alive_if_empty is true, then it'll be mono 44.1khz silence -- otherwise it doesn't matter what it is
+            SILENCE_CHANNELS
+        }
     }
 
     #[inline]
     fn sample_rate(&self) -> SampleRate {
-        self.current.sample_rate()
+        // current_span_len() should never return 0 unless the source is empty, so this is a cheeky hint
+        if self.current.current_span_len() != Some(0) {
+            self.current.sample_rate()
+        } else if let Some((next, _)) = self.input.next_sounds.lock().unwrap().first() {
+            next.sample_rate()
+        } else {
+            // If keep_alive_if_empty is true, then it'll be mono 44.1khz silence -- otherwise it doesn't matter what it is
+            SILENCE_SAMPLE_RATE
+        }
     }
 
     #[inline]
@@ -221,7 +239,11 @@ impl SourcesQueueOutput {
             let mut next = self.input.next_sounds.lock().unwrap();
 
             if next.is_empty() {
-                let silence = Box::new(Zero::new_samples(nz!(1), nz!(44100), THRESHOLD)) as Box<_>;
+                let silence = Box::new(Zero::new_samples(
+                    SILENCE_CHANNELS,
+                    SILENCE_SAMPLE_RATE,
+                    THRESHOLD,
+                )) as Box<_>;
                 if self.input.keep_alive_if_empty.load(Ordering::Acquire) {
                     // Play a short silence in order to avoid spinlocking.
                     (silence, None)
@@ -247,7 +269,6 @@ mod tests {
     use crate::source::Source;
 
     #[test]
-    #[ignore] // FIXME: samples rate and channel not updated immediately after transition
     fn basic() {
         let (tx, mut rx) = queue::queue(false);
 

src/source/skip.rs

@@ -39,18 +39,22 @@ where
             return;
         }
 
-        let ns_per_sample: u128 =
-            NS_PER_SECOND / input.sample_rate().get() as u128 / input.channels().get() as u128;
+        let sample_rate = input.sample_rate().get() as u128;
+        let channels = input.channels().get() as u128;
+
+        let samples_per_channel = duration.as_nanos() * sample_rate / NS_PER_SECOND;
+        let samples_to_skip: u128 = samples_per_channel * channels;
 
         // Check if we need to skip only part of the current span.
-        if span_len as u128 * ns_per_sample > duration.as_nanos() {
-            skip_samples(input, (duration.as_nanos() / ns_per_sample) as usize);
+        if span_len as u128 > samples_to_skip {
+            skip_samples(input, samples_to_skip as usize);
             return;
         }
 
+        duration -= Duration::from_nanos(
+            (NS_PER_SECOND * span_len as u128 / channels / sample_rate) as u64,
+        );
         skip_samples(input, span_len);
-
-        duration -= Duration::from_nanos((span_len * ns_per_sample as usize) as u64);
     }
 }