From 7bf80663dc81b4d50cd90b584d3dd334578a68b2 Mon Sep 17 00:00:00 2001
From: Diego Lopes <diego95lopes@live.com>
Date: Wed, 14 Oct 2026 13:45:13 -0400
Subject: [PATCH 1/2] Fix resampler edge read at device/session rate mismatch

The output resampler interpolated toward a stale sample at the end of every
mix block when the device rate differs from the session rate. It now holds
the last valid sample.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
---
 crates/playback/src/lib.rs | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/crates/playback/src/lib.rs b/crates/playback/src/lib.rs
index b945d4b6..fc3b6a4e 100644
--- a/crates/playback/src/lib.rs
+++ b/crates/playback/src/lib.rs
@@ -362,7 +362,9 @@ impl AudioState {
             let sample = |c: usize| {
                 let ch = self.pending.get(c);
                 let a = ch.and_then(|v| v.get(i0)).copied().unwrap_or(0.0);
-                let b = ch.and_then(|v| v.get(i0 + 1)).copied().unwrap_or(a);
+                // Holds the last sample at the block edge (`pending` is BLOCK long,
+                // only `pending_len` is valid); carry the next block's first sample if audible.
+                let b = if i0 + 1 < self.pending_len { ch.and_then(|v| v.get(i0 + 1)).copied().unwrap_or(a) } else { a };
                 a + (b - a) * fr
             };
             if nch > 2 && channels < nch {

From dfde8a672474331051084510ea81b70a9d68592c Mon Sep 17 00:00:00 2001
From: Diego Lopes <diego95lopes@live.com>
Date: Mon, 19 Oct 2026 23:36:00 -0400
Subject: [PATCH 2/2] Add regression test for the resampler block edge

Render a long DC block, then short blocks of silence with the device
rate below the session rate. The interpolation must not read the stale
frame past pending_len. Also correct the comment on the edge hold.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 crates/playback/src/lib.rs | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/crates/playback/src/lib.rs b/crates/playback/src/lib.rs
index f5023feb..92823286 100644
--- a/crates/playback/src/lib.rs
+++ b/crates/playback/src/lib.rs
@@ -362,8 +362,7 @@ impl AudioState {
             let sample = |c: usize| {
                 let ch = self.pending.get(c);
                 let a = ch.and_then(|v| v.get(i0)).copied().unwrap_or(0.0);
-                // Holds the last sample at the block edge (`pending` is BLOCK long,
-                // only `pending_len` is valid); carry the next block's first sample if audible.
+                // `pending` is BLOCK long; only `pending_len` frames are valid. Hold the last one at the edge.
                 let b = if i0 + 1 < self.pending_len { ch.and_then(|v| v.get(i0 + 1)).copied().unwrap_or(a) } else { a };
                 a + (b - a) * fr
             };
@@ -1216,6 +1215,26 @@ mod tests {
         }
     }
 
+    #[test]
+    fn resampling_at_a_short_block_edge_does_not_mix_in_stale_frames() {
+        use soundcraft_model::ChannelFormat;
+        // DC for the first long block, then silence. The device runs slower than the session, so
+        // reads land between frames; a short block leaves the long block's DC past `pending_len`.
+        let mut st = audio_output_state(ChannelFormat::Stereo, vec![vec![0.8; BLOCK]; 2]);
+        st.device_rate = 44_100.0;
+        let mut long = vec![0.0; 2 * 470];
+        st.fill(&mut long, 2);
+        assert_eq!(st.pending_len, BLOCK);
+        let mut short = [0.0; 2 * 8];
+        for call in 0..20 {
+            st.fill(&mut short, 2);
+            assert!(st.pending_len < BLOCK);
+            // The first frame of the first short call still reads the DC block's last frame.
+            let from = if call == 0 { 2 } else { 0 };
+            assert!(short[from..].iter().all(|x| x.abs() < 1e-6), "call {call}: {short:?}");
+        }
+    }
+
     #[test]
     fn mono_device_preserves_centered_mono_level_and_includes_surround_right_channels() {
         use soundcraft_model::ChannelFormat;