From 72b4a1637837e6235a1cde14d776cbde3e022e8d Mon Sep 17 00:00:00 2001
From: Alexander Shabarshov <unclshura@gmail.com>
Date: Sat, 25 Jul 2026 11:02:03 +0100
Subject: [PATCH] Fixed mono stems mixing

---
 ABStemPlayer/Views/PlaybackControls.axaml   | 48 +++++++--------------
 AudioCore/Impl/AudioMixer.cs                | 26 ++++++++---
 AudioCore/Impl/StemPlaybackEngine.cs        | 12 +++++-
 AudioCore_Tests/AudioMixer_Tests.cs         |  2 +-
 AudioCore_Tests/StemPlaybackEngine_Tests.cs |  4 +-
 5 files changed, 50 insertions(+), 42 deletions(-)

diff --git a/ABStemPlayer/Views/PlaybackControls.axaml b/ABStemPlayer/Views/PlaybackControls.axaml
index 8122128..cf8fa64 100644
--- a/ABStemPlayer/Views/PlaybackControls.axaml
+++ b/ABStemPlayer/Views/PlaybackControls.axaml
@@ -194,49 +194,33 @@
                                   Margin="0,0,6,0"/>
 
                     <Button Command="{Binding SetPointACommand}"
-                            Width="60"
-                            Height="32"
+                            Width="40"
+                            Height="40"
                             Grid.Column="1"
                             Margin="0,0,6,0">
                         <Grid>
                             <Path Fill="#0080ff"
-                                  Data="M 30 6 L 46 18 L 38 18 L 38 26 L 22 26 L 22 18 L 14 18 Z"/>
-                            <Path Stroke="#e0e0e0"
-                                  StrokeThickness="2"
-                                  Fill="Transparent"
-                                  Data="M 20 5 L 34 35 H 28 L 25 25 H 15 L 12 35 H 6 Z M 20 13 L 17 21 H 23 Z"/>
+                                  Data="M 26 8 
+L 26 32 
+L 14 32 
+L 24 20 
+L 14 8 
+L 26 8" />
                         </Grid>
                     </Button>
 
                     <Button Command="{Binding SetPointBCommand}"
-                            Width="60"
-                            Height="32"
+                            Width="40"
+                            Height="40"
                             Grid.Column="2">
                         <Grid>
                             <Path Fill="#0080ff"
-                                  Data="M 30 26 L 46 14 L 38 14 L 38 6 L 22 6 L 22 14 L 14 14 Z"/>
-                            <Path Stroke="#e0e0e0"
-                                  StrokeThickness="2"
-                                  Fill="Transparent"
-                                  Data="
-                                  M 10 2.44 L 18.4 2.44
-                                  A 6 6 0 0 1 24.4 8.44
-                                  A 6 6 0 0 1 18.4 14.44
-                                  L 22 14.44
-                                  A 5.4 5.4 0 0 1 27.4 19.84
-                                  A 5.4 5.4 0 0 1 22 25.24
-                                  L 10 25.24 Z
-
-                                  M 19 7.24 L 19 10.44
-                                  L 25 10.44
-                                  A 1.2 1.2 0 0 0 26.2 9.24
-                                  A 1.2 1.2 0 0 0 25 7.24 Z
-
-                                  M 19 14.44 L 19 19.04
-                                  L 25 19.04
-                                  A 1.8 1.8 0 0 0 26.8 17.24
-                                  A 1.8 1.8 0 0 0 25 14.44 Z
-                                  "/>
+                                  Data="M 14 8
+L 14 32
+L 26 32
+L 16 20
+L 26 8
+L 14 8"/>
                         </Grid>
                     </Button>
                 </Grid>
diff --git a/AudioCore/Impl/AudioMixer.cs b/AudioCore/Impl/AudioMixer.cs
index 1765f0a..74ce338 100644
--- a/AudioCore/Impl/AudioMixer.cs
+++ b/AudioCore/Impl/AudioMixer.cs
@@ -50,18 +50,34 @@ public sealed class AudioMixer : IAudioMixer
 
             for (var i = 0; i < frames; i++)
             {
-                if (i * inChannels + 1 >= inSpan.Length)
+                var baseIndex = i * inChannels;
+
+                // If there are no samples for this frame, skip
+                if (baseIndex >= inSpan.Length)
                 {
                     outSpan[i * 2 + 0] = 0f;
                     outSpan[i * 2 + 1] = 0f;
                     continue;
                 }
 
-                var l = inChannels > 1 ? inSpan[i * inChannels + 0] : inSpan[i];
-                var r = inChannels > 1 ? inSpan[i * inChannels + 1] : inSpan[i];
+                if (inChannels == 1)
+                {
+                    var inp = inSpan[baseIndex];
+                    outSpan[i * 2 + 0] += inp * leftGain;
+                    outSpan[i * 2 + 1] += inp * rightGain;
+                }
+                else
+                {
+                    // ensure both left and right samples exist for multi-channel input
+                    if (baseIndex + 1 >= inSpan.Length)
+                        continue; // or treat missing right as 0, depending on desired behavior
 
-                outSpan[i * 2 + 0] += l * leftGain;
-                outSpan[i * 2 + 1] += r * rightGain;
+                    var l = inSpan[baseIndex + 0];
+                    var r = inSpan[baseIndex + 1];
+
+                    outSpan[i * 2 + 0] += l * leftGain;
+                    outSpan[i * 2 + 1] += r * rightGain;
+                }
             }
         }
 
diff --git a/AudioCore/Impl/StemPlaybackEngine.cs b/AudioCore/Impl/StemPlaybackEngine.cs
index c1ae79e..ccfc513 100644
--- a/AudioCore/Impl/StemPlaybackEngine.cs
+++ b/AudioCore/Impl/StemPlaybackEngine.cs
@@ -343,9 +343,17 @@ public sealed class StemPlaybackEngine : IStemPlaybackEngine, IDisposable
 
                 if (loopEnabled && loopEnd > loopStart && nextPosition >= loopEnd)
                 {
+                    // Rewind decoders to the loop start and continue decoding so playback loops
+                    foreach (var d in decodersSnapshot)
+                    {
+                        try { d.Seek(loopStart); } catch { }
+                    }
+
                     lock (_stateLock)
-                        _decodedFramePosition = loopEnd;
-                    break;
+                        _decodedFramePosition = loopStart;
+
+                    // continue decoding from the loop start
+                    continue;
                 }
 
                 lock (_stateLock)
diff --git a/AudioCore_Tests/AudioMixer_Tests.cs b/AudioCore_Tests/AudioMixer_Tests.cs
index 7256a44..caec258 100644
--- a/AudioCore_Tests/AudioMixer_Tests.cs
+++ b/AudioCore_Tests/AudioMixer_Tests.cs
@@ -147,7 +147,7 @@ public sealed class AudioMixer_Tests
 
     [TestMethod]
     [TestCategory("ProductionBugSuspected")]
-    [Ignore("ProductionBugSuspected")]
+    //[Ignore("ProductionBugSuspected")]
     public void Mixer_Handles_Mono_Stem()
     {
         // mono block
diff --git a/AudioCore_Tests/StemPlaybackEngine_Tests.cs b/AudioCore_Tests/StemPlaybackEngine_Tests.cs
index f40eb95..f52f9b1 100644
--- a/AudioCore_Tests/StemPlaybackEngine_Tests.cs
+++ b/AudioCore_Tests/StemPlaybackEngine_Tests.cs
@@ -302,7 +302,7 @@ public sealed class StemPlaybackEngine_Tests
     public async Task LoopRegion_SeeksBackOnBoundary()
     {
         var pool          = new AudioBufferPool();
-        var decoderFactory = new MockDecoderFactory(pool, 1024, 5);
+        var decoderFactory = new MockDecoderFactory(pool, 44100, 5);
         var output        = new MockOutput();
         var mixer         = new MockMixer(pool);
         var stretch       = new MockTimeStretch();
@@ -320,7 +320,7 @@ public sealed class StemPlaybackEngine_Tests
         await engine.LoadSessionAsync(session, new DummyProgressReporter());
         await engine.PlayAsync();
 
-        await Task.Delay(TimeSpan.FromSeconds(3));
+        await Task.Delay(TimeSpan.FromSeconds(6));
 
         await engine.StopAsync();