Fix 1-sample channel shift (L/R swap) bug when rapidly appending stereo sources to an empty player queue

CHANGELOG.md

@@ -27,7 +27,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Improved queue, buffer, mixer and sample rate conversion performance.
 
 ### Fixed
-
+- Fixed a 1-sample channel shift (L/R swap) in Player when rapidly appending stereo sources to an empty queue.
 - Fixed `Player::skip_one` not decreasing the player's length immediately.
 - Fixed `Source::current_span_len()` to consistently return total span length.
 - Fixed `Source::size_hint()` to consistently report actual bounds based on current sources.

src/queue.rs

@@ -394,8 +394,8 @@ mod tests {
             let (tx, rx) = queue::queue(keep_alive);
             assert_eq!(
                 rx.channels(),
-                nz!(1),
-                "Initial channels should be 1 (keep_alive={keep_alive})"
+                nz!(2),
+                "Initial channels should be 2 (keep_alive={keep_alive})"
             );
             assert_eq!(
                 rx.sample_rate(),

src/source/empty.rs

@@ -42,7 +42,7 @@ impl Source for Empty {
 
     #[inline]
     fn channels(&self) -> ChannelCount {
-        nz!(1)
+        nz!(2) // Default to 2 (stereo) to prevent a 1-sample channel shifting bug in the Queue when swapping to stereo sources.
     }
 
     #[inline]