Refactor playback speed & mixer management; UI tweaks

Refactor playback speed and mixer settings to be managed via PlaybackSession, removing SetSpeed/SetStem* methods. Update Play command to apply current mixer and speed. Optimize RenderLoop with reusable audio block list and conditional output start. Align playback control icons in XAML. Update tests for new speed handling and add speed decrease coverage. Remove unused IStemPlaybackEngine methods.

ABStemPlayer/ViewModels/PlaybackViewModel.cs

@@ -67,28 +67,28 @@ public sealed partial class PlaybackViewModel : ObservableObject
         IStemWaveformService waveformService
         )
     {
-        _engine          = engine;
+        _engine                 = engine;
-        _separator       = separator;
+        _separator              = separator;
-        _decoderFactory  = decoderFactory;
+        _decoderFactory         = decoderFactory;
-        _waveformService = waveformService;
+        _waveformService        = waveformService;
 
         CancelConversionCommand = new RelayCommand(_ => CancelConversion());
 
         OpenFileCommand         = new AsyncRelayCommand(OpenFileAsync);
-        PlayCommand             = new AsyncRelayCommand(() => _engine.PlayAsync());
+        PlayCommand             = new AsyncRelayCommand(OnPlay);
         PauseCommand            = new AsyncRelayCommand(() => _engine.PauseAsync());
         StopCommand             = new AsyncRelayCommand(async () => { await _engine.StopAsync(); await _engine.SeekAsync(TimeSpan.Zero); });
 
         RewindCommand           = new AsyncRelayCommand(() => _engine.SeekAsync(CurrentTime - TimeSpan.FromSeconds(5)));
         FastForwardCommand      = new AsyncRelayCommand(() => _engine.SeekAsync(CurrentTime + TimeSpan.FromSeconds(5)));
 
-        SetPointACommand        = new RelayCommand(_ =>
+        SetPointACommand = new RelayCommand(_ =>
         {
             _loopA = CurrentTime;
             UpdateLoop();
         });
 
-        SetPointBCommand        = new RelayCommand(_ =>
+        SetPointBCommand = new RelayCommand(_ =>
         {
             _loopB = CurrentTime;
             UpdateLoop();
@@ -97,6 +97,24 @@ public sealed partial class PlaybackViewModel : ObservableObject
 
     }
 
+    private async Task OnPlay()
+    {
+        if (_engine.CurrentSession == null)
+            return;
+
+        var mixer = new MixerSettings
+        {
+            Stems = _engine.CurrentSession.StemSet.Stems.Select(GetMixerSettings).ToList()
+        };
+
+        _engine.CurrentSession.Mixer = mixer;
+        _engine.CurrentSession.Speed = new PlaybackSpeedSettings
+        {
+            Speed = PlaybackSpeed
+        };
+        await _engine.PlayAsync();
+    }
+
     partial void OnCurrentTimeChanged(TimeSpan value)
     {
         foreach (var band in Bands)
@@ -112,6 +130,12 @@ public sealed partial class PlaybackViewModel : ObservableObject
             band.UpdatePlaybackPosition(CurrentTime, TotalTime);
         }
     }
+
+    partial void OnPlaybackSpeedChanged(float value)
+    {
+        _engine.CurrentSession?.Speed.Speed = value;
+    }
+
     // -----------------------------
     // File open + stem conversion
     //------------------------------
@@ -358,18 +382,18 @@ public sealed partial class PlaybackViewModel : ObservableObject
         if ( found != null )
             return new StemMixSettings
             {
-                GainDb = found.GainDb,
+                GainDb  = found.GainDb,
                 Enabled = found.Enabled,
-                Pan = found.Pan
+                Pan     = found.Pan
             };
 
         found = new StemChannelViewModel(stem.Type);
         Mixer.Stems.Add(found);
         return new StemMixSettings
         {
-            GainDb = found.GainDb,
+            GainDb  = found.GainDb,
             Enabled = found.Enabled,
-            Pan = found.Pan
+            Pan     = found.Pan
         };
     }
 
@@ -402,8 +426,4 @@ public sealed partial class PlaybackViewModel : ObservableObject
         }
     }
 
-    public void UpdateSpeed()
-    {
-        _engine.SetSpeed(PlaybackSpeed);
-    }
 }

ABStemPlayer/Views/PlaybackControls.axaml

@@ -40,7 +40,16 @@
                             Grid.Column="0"
                             Margin="0,0,6,0">
                         <Path Fill="#e0e0e0"
-                              Data="M 6 10 H 18 L 22 14 H 34 V 30 H 6 Z"/>
+                              Stretch="None"
+                              RenderTransformOrigin="0,0">
+                            <Path.RenderTransform>
+                                <TranslateTransform X="-8" Y="-8"/>
+                            </Path.RenderTransform>
+
+                            <Path.Data>
+                                M 6 10 H 18 L 22 14 H 34 V 30 H 6 Z
+                            </Path.Data>
+                        </Path>
                     </Button>
 
                     <!-- Rewind -->
@@ -50,7 +59,16 @@
                             Grid.Column="1"
                             Margin="0,0,6,0">
                         <Path Fill="#e0e0e0"
-                              Data="M 30 8 L 10 20 L 30 32 Z M 18 8 L -2 20 L 18 32 Z"/>
+                              Stretch="None"
+                              RenderTransformOrigin="0,0">
+                            <Path.RenderTransform>
+                                <TranslateTransform X="-6" Y="-8"/>
+                            </Path.RenderTransform>
+
+                            <Path.Data>
+                                M 30 8 L 10 20 L 30 32 Z M 18 8 L -2 20 L 18 32 Z
+                            </Path.Data>
+                        </Path>
                     </Button>
 
                     <!-- Play -->
@@ -59,8 +77,17 @@
                             Height="40"
                             Grid.Column="2"
                             Margin="0,0,6,0">
-                        <Path Fill="#00ff00"
+                        <Path Fill="#e0e0e0"
-                              Data="M 10 8 L 32 20 L 10 32 Z"/>
+                              Stretch="None"
+                              RenderTransformOrigin="0,0">
+                            <Path.RenderTransform>
+                                <TranslateTransform X="-8" Y="-8"/>
+                            </Path.RenderTransform>
+
+                            <Path.Data>
+                                M 10 8 L 32 20 L 10 32 Z
+                            </Path.Data>
+                        </Path>
                     </Button>
 
                     <!-- Pause -->
@@ -70,9 +97,18 @@
                             Grid.Column="3"
                             Margin="0,0,6,0">
                         <Path Fill="#e0e0e0"
-                              Data="M 8 8 H 16 V 32 H 8 Z
+                              Stretch="None"
-                                    M 24 8 H 32 V 32 H 24 Z"/>
+                              RenderTransformOrigin="0,0">
-                    </Button>
+                            <Path.RenderTransform>
+                                <TranslateTransform X="-8" Y="-8"/>
+                            </Path.RenderTransform>
+
+                            <Path.Data>
+                                M 8 8 H 16 V 32 H 8 Z
+                                M 24 8 H 32 V 32 H 24 Z
+                            </Path.Data>
+                        </Path>
+                </Button>
 
                     <!-- Stop -->
                     <Button Command="{Binding StopCommand}"
@@ -81,7 +117,16 @@
                             Grid.Column="4"
                             Margin="0,0,6,0">
                         <Path Fill="#e0e0e0"
-                              Data="M 8 8 H 32 V 32 H 8 Z"/>
+                              Stretch="None"
+                              RenderTransformOrigin="0,0">
+                            <Path.RenderTransform>
+                                <TranslateTransform X="-8" Y="-8"/>
+                            </Path.RenderTransform>
+
+                            <Path.Data>
+                                M 8 8 H 32 V 32 H 8 Z
+                            </Path.Data>
+                        </Path>
                     </Button>
 
                     <!-- Fast Forward -->
@@ -90,7 +135,16 @@
                             Height="40"
                             Grid.Column="5">
                         <Path Fill="#e0e0e0"
-                              Data="M 10 8 L 30 20 L 10 32 Z M 22 8 L 42 20 L 22 32 Z"/>
+                              Stretch="None"
+                              RenderTransformOrigin="0,0">
+                            <Path.RenderTransform>
+                                <TranslateTransform X="-14" Y="-8"/>
+                            </Path.RenderTransform>
+
+                            <Path.Data>
+                                M 10 8 L 30 20 L 10 32 Z M 22 8 L 42 20 L 22 32 Z
+                            </Path.Data>
+                        </Path>
                     </Button>
                 </Grid>
 
@@ -165,23 +219,23 @@
                                   StrokeThickness="2"
                                   Fill="Transparent"
                                   Data="
-                                    M 10 2.44 L 18.4 2.44
+                                  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 24.4 8.44
-                                    A 6 6 0 0 1 18.4 14.44
+                                  A 6 6 0 0 1 18.4 14.44
-                                    L 22 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 27.4 19.84
-                                    A 5.4 5.4 0 0 1 22 25.24
+                                  A 5.4 5.4 0 0 1 22 25.24
-                                    L 10 25.24 Z
+                                  L 10 25.24 Z
 
-                                    M 19 7.24 L 19 10.44
+                                  M 19 7.24 L 19 10.44
-                                    L 25 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 26.2 9.24
-                                    A 1.2 1.2 0 0 0 25 7.24 Z
+                                  A 1.2 1.2 0 0 0 25 7.24 Z
 
-                                    M 19 14.44 L 19 19.04
+                                  M 19 14.44 L 19 19.04
-                                    L 25 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 26.8 17.24
-                                    A 1.8 1.8 0 0 0 25 14.44 Z
+                                  A 1.8 1.8 0 0 0 25 14.44 Z
                                   "/>
                         </Grid>
                     </Button>

AudioCore/Impl/RubberBandTimeStretchEngine.cs

@@ -115,23 +115,23 @@ public sealed class RubberBandTimeStretchEngine : ITimeStretchEngine, IDisposabl
         {
             FileName = "ffmpeg",
             Arguments =
-            $"-hide_banner -loglevel error " +
+                $"-hide_banner -loglevel error " +
-            $"-f f32le -ar {_sampleRate} -ac {_channels} -i pipe:0 " +
+                $"-f f32le -ar {_sampleRate} -ac {_channels} -i pipe:0 " +
-            $"-af \"rubberband=tempo={_speed}\" " +
+                $"-af \"rubberband=tempo={_speed}\" " +
-            $"-f f32le -ar {_sampleRate} -ac {_channels} pipe:1",
+                $"-f f32le -ar {_sampleRate} -ac {_channels} pipe:1",
-            RedirectStandardInput = true,
+            RedirectStandardInput  = true,
             RedirectStandardOutput = true,
-            UseShellExecute = false,
+            UseShellExecute        = false,
-            CreateNoWindow = true,
+            CreateNoWindow         = true,
-            WindowStyle = ProcessWindowStyle.Hidden,
+            WindowStyle            = ProcessWindowStyle.Hidden,
         };
 
-        _ff = System.Diagnostics.Process.Start(psi);
+        _ff     = System.Diagnostics.Process.Start(psi);
-        _stdin = _ff!.StandardInput.BaseStream;
+        _stdin  = _ff!.StandardInput.BaseStream;
         _stdout = _ff!.StandardOutput.BaseStream;
 
         _readerRunning = true;
-        _readerThread = new Thread(ReaderLoop) { IsBackground = true };
+        _readerThread  = new Thread(ReaderLoop) { IsBackground = true };
         _readerThread.Start();
     }
 

AudioCore/Impl/StemPlaybackEngine.cs

@@ -12,10 +12,8 @@ public sealed class StemPlaybackEngine : IStemPlaybackEngine, IDisposable
     private PlaybackSession?             _session;
     private IStemDecoder[]               _decoders        = Array.Empty<IStemDecoder>();
 
-    private StemMixSettings[]            _stemMixSettings = Array.Empty<StemMixSettings>();
+    private MixerSettings? Mixer => _session?.Mixer;
-    private MixerSettings?               _mixerSettings;
 
-    private PlaybackSpeedSettings        _speedSettings   = new();
     private LoopRegion                   _loopRegion      = new();
 
     private long                         _currentFramePosition;
@@ -23,10 +21,14 @@ public sealed class StemPlaybackEngine : IStemPlaybackEngine, IDisposable
     private long                         _loopEndFrames;
 
     private bool                         _isPlaying;
+    private bool                         _outputStarted;
     private CancellationTokenSource?     _renderCts;
     private Task?                        _renderTask;
     private IProgressReporter<TimeSpan>? _progressReporter;
 
+    // Reused per-block list, no per-frame allocation
+    private readonly List<AudioBlock>    _stemBlocks      = new(8);
+
     public StemPlaybackEngine(
         IStemDecoderFactory stemDecoderFactory,
         IAudioOutputDevice outputDevice,
@@ -34,9 +36,9 @@ public sealed class StemPlaybackEngine : IStemPlaybackEngine, IDisposable
         ITimeStretchEngine timeStretchEngine)
     {
         _stemDecoderFactory = stemDecoderFactory;
-        _outputDevice       = outputDevice;
+        _outputDevice = outputDevice;
-        _audioMixer         = audioMixer;
+        _audioMixer = audioMixer;
-        _timeStretchEngine  = timeStretchEngine;
+        _timeStretchEngine = timeStretchEngine;
     }
 
     public PlaybackSession? CurrentSession
@@ -50,7 +52,7 @@ public sealed class StemPlaybackEngine : IStemPlaybackEngine, IDisposable
         }
     }
 
-    public async Task LoadSessionAsync(PlaybackSession session, IProgressReporter<TimeSpan  > progress)
+    public async Task LoadSessionAsync(PlaybackSession session, IProgressReporter<TimeSpan> progress)
     {
         await StopAsync().ConfigureAwait(false);
 
@@ -63,17 +65,7 @@ public sealed class StemPlaybackEngine : IStemPlaybackEngine, IDisposable
                 .Select(stem => _stemDecoderFactory.Create(stem))
                 .ToArray();
 
-            _stemMixSettings = session.Mixer.Stems.ToArray();
+            _timeStretchEngine.Configure(_session.Speed);
-            _mixerSettings = new MixerSettings
-            {
-                Stems = _stemMixSettings
-            };
-
-            _speedSettings = new PlaybackSpeedSettings
-            {
-                Speed = session.Speed.Speed
-            };
-            _timeStretchEngine.Configure(_speedSettings);
 
             _loopRegion = session.Loop;
             if (_loopRegion.IsEnabled)
@@ -109,11 +101,11 @@ public sealed class StemPlaybackEngine : IStemPlaybackEngine, IDisposable
             {
                 _renderCts?.Dispose();
                 _renderCts = new CancellationTokenSource();
+                _outputStarted = false;
                 _renderTask = Task.Run(() => RenderLoopAsync(_renderCts.Token));
             }
 
             _isPlaying = true;
-            _outputDevice.Start();
         }
 
         return Task.CompletedTask;
@@ -129,7 +121,12 @@ public sealed class StemPlaybackEngine : IStemPlaybackEngine, IDisposable
             }
 
             _isPlaying = false;
-            _outputDevice.Stop();
+
+            if (_outputStarted)
+            {
+                _outputDevice.Stop();
+                _outputStarted = false;
+            }
         }
 
         return Task.CompletedTask;
@@ -140,6 +137,7 @@ public sealed class StemPlaybackEngine : IStemPlaybackEngine, IDisposable
         CancellationTokenSource? ctsToCancel;
         IStemDecoder[] decodersToDispose;
         Task? renderTask;
+        bool outputStarted;
 
         lock (_stateLock)
         {
@@ -154,7 +152,13 @@ public sealed class StemPlaybackEngine : IStemPlaybackEngine, IDisposable
             ctsToCancel = _renderCts;
             _renderCts = null;
 
-            _outputDevice.Stop();
+            outputStarted = _outputStarted;
+            _outputStarted = false;
+
+            if (outputStarted)
+            {
+                _outputDevice.Stop();
+            }
 
             decodersToDispose = _decoders;
             _decoders = Array.Empty<IStemDecoder>();
@@ -168,9 +172,7 @@ public sealed class StemPlaybackEngine : IStemPlaybackEngine, IDisposable
             ctsToCancel.Cancel();
         }
 
-        // Do NOT wait on renderTask if we are already inside it.
+        if (renderTask is not null && renderTask.Id != Task.CurrentId)
-        // Just let it observe cancellation and exit.
-        if (renderTask is not null && !ReferenceEquals(renderTask, Task.CurrentId))
         {
             try
             {
@@ -241,72 +243,6 @@ public sealed class StemPlaybackEngine : IStemPlaybackEngine, IDisposable
         }
     }
 
-    public void SetSpeed(double speedFactor)
-    {
-        lock (_stateLock)
-        {
-            _speedSettings.Speed = (float)speedFactor;
-            _timeStretchEngine.Configure(_speedSettings);
-        }
-    }
-
-    public void SetStemEnabled(int stemIndex, bool enabled)
-    {
-        lock (_stateLock)
-        {
-            if (stemIndex < 0 || stemIndex >= _stemMixSettings.Length)
-            {
-                return;
-            }
-
-            var current = _stemMixSettings[stemIndex];
-            _stemMixSettings[stemIndex] = new StemMixSettings
-            {
-                Enabled = enabled,
-                GainDb = current.GainDb,
-                Pan = current.Pan
-            };
-        }
-    }
-
-    public void SetStemGain(int stemIndex, float gainDb)
-    {
-        lock (_stateLock)
-        {
-            if (stemIndex < 0 || stemIndex >= _stemMixSettings.Length)
-            {
-                return;
-            }
-
-            var current = _stemMixSettings[stemIndex];
-            _stemMixSettings[stemIndex] = new StemMixSettings
-            {
-                Enabled = current.Enabled,
-                GainDb = gainDb,
-                Pan = current.Pan
-            };
-        }
-    }
-
-    public void SetStemPan(int stemIndex, float pan)
-    {
-        lock (_stateLock)
-        {
-            if (stemIndex < 0 || stemIndex >= _stemMixSettings.Length)
-            {
-                return;
-            }
-
-            var current = _stemMixSettings[stemIndex];
-            _stemMixSettings[stemIndex] = new StemMixSettings
-            {
-                Enabled = current.Enabled,
-                GainDb = current.GainDb,
-                Pan = pan
-            };
-        }
-    }
-
     private async Task RenderLoopAsync(CancellationToken ct)
     {
         try
@@ -315,51 +251,56 @@ public sealed class StemPlaybackEngine : IStemPlaybackEngine, IDisposable
             {
                 bool playing;
                 IStemDecoder[] decodersSnapshot;
-                MixerSettings? mixerSettingsSnapshot;
                 long loopStart;
                 long loopEnd;
                 bool loopEnabled;
+                MixerSettings? mixerSnapshot;
+                IProgressReporter<TimeSpan>? progressReporter;
 
                 lock (_stateLock)
                 {
-                    playing               = _isPlaying;
+                    playing = _isPlaying;
-                    decodersSnapshot      = _decoders;
+                    decodersSnapshot = _decoders;
-                    mixerSettingsSnapshot = _mixerSettings;
+                    loopStart = _loopStartFrames;
-                    loopStart             = _loopStartFrames;
+                    loopEnd = _loopEndFrames;
-                    loopEnd               = _loopEndFrames;
+                    loopEnabled = _loopRegion.IsEnabled;
-                    loopEnabled           = _loopRegion.IsEnabled;
+                    mixerSnapshot = Mixer;
+                    progressReporter = _progressReporter;
                 }
 
-                if (!playing || decodersSnapshot.Length == 0 || mixerSettingsSnapshot is null)
+                if (!playing || decodersSnapshot.Length == 0 || mixerSnapshot is null)
                 {
                     await Task.Delay(5, ct).ConfigureAwait(false);
                     continue;
                 }
 
-                List<AudioBlock> stemBlocks = new();
+                _stemBlocks.Clear();
-
+                var eofDetected = false;
-                bool eofDetected = false;
-
-                // Decode once, no double scanning
-                var totalFrames = decodersSnapshot[0].Stem.Duration.TotalSeconds * _outputDevice.SampleRate;
 
                 foreach (var decoder in decodersSnapshot)
                 {
                     if (!decoder.TryDecodeNextBlock(out var block))
                     {
                         eofDetected = true;
-                        foreach (var b in stemBlocks)
+
-                            b.Dispose();
+                        for (var i = 0; i < _stemBlocks.Count; i++)
+                        {
+                            _stemBlocks[i].Dispose();
+                        }
+
+                        _stemBlocks.Clear();
                         break;
                     }
 
-                    stemBlocks.Add(block);
+                    _stemBlocks.Add(block);
                 }
 
-                if (eofDetected || stemBlocks.Count == 0)
+                if (eofDetected || _stemBlocks.Count == 0)
                 {
-                    // Report EOF progress
+                    if (progressReporter is not null)
-                    await _progressReporter!.ReportProgress(TimeSpan.FromSeconds(1.0));
+                    {
+                        await progressReporter.ReportProgress(TimeSpan.FromSeconds(1.0));
+                    }
 
                     lock (_stateLock)
                     {
@@ -369,34 +310,45 @@ public sealed class StemPlaybackEngine : IStemPlaybackEngine, IDisposable
                     break;
                 }
 
-                // Report progress (0..1)
                 var progress = TimeSpan.FromSeconds((double)_currentFramePosition / _outputDevice.SampleRate);
-                await _progressReporter!.ReportProgress(progress);
+                if (progressReporter is not null)
-
-                using var mixed = _audioMixer.Mix(stemBlocks, mixerSettingsSnapshot);
-
-                foreach (var block in stemBlocks)
-                    block.Dispose();
-
-                var nextPosition = mixed.SamplePosition + mixed.Frames;
-
-                // Loop region handling
-                if (loopEnabled && loopEnd > loopStart && nextPosition >= loopEnd)
                 {
-                    foreach (var decoder in decodersSnapshot)
+                    await progressReporter.ReportProgress(progress);
-                        decoder.Seek(loopStart);
-
-                    lock (_stateLock)
-                    {
-                        _currentFramePosition = loopStart;
-                    }
-
-                    continue;
                 }
 
+                using var mixed = _audioMixer.Mix(_stemBlocks, mixerSnapshot);
+
+                for (var i = 0; i < _stemBlocks.Count; i++)
+                {
+                    _stemBlocks[i].Dispose();
+                }
+                _stemBlocks.Clear();
+
                 using var stretched = _timeStretchEngine.Process(mixed);
 
-                _outputDevice.Write(stretched.Buffer.Span);
+                if (stretched.Buffer != null)
+                {
+                    if (!_outputStarted)
+                    {
+                        _outputDevice.Start();
+                        _outputStarted = true;
+                    }
+
+                    _outputDevice.Write(stretched.Buffer.Span);
+                }
+
+                var nextPosition = mixed.SamplePosition + mixed.Frames;
+
+                if (loopEnabled && loopEnd > loopStart && nextPosition >= loopEnd)
+                {
+                    lock (_stateLock)
+                    {
+                        _currentFramePosition = loopEnd;
+                        _isPlaying = false;
+                    }
+
+                    break;
+                }
 
                 lock (_stateLock)
                 {
@@ -406,7 +358,11 @@ public sealed class StemPlaybackEngine : IStemPlaybackEngine, IDisposable
         }
         finally
         {
-            _outputDevice.Stop();
+            if (_outputStarted)
+            {
+                _outputDevice.Stop();
+                _outputStarted = false;
+            }
         }
     }
 

AudioCore/Impl/WasapiOutputDevice.cs

@@ -28,6 +28,7 @@ public sealed class WasapiOutputDevice : IAudioOutputDevice, IDisposable
     {
         _pool      = pool;
         _mixFormat = WaveFormat.CreateIeeeFloatWaveFormat(sampleRate, channels);
+        _isFloat   = true;
         SampleRate = sampleRate;
         Channels   = channels;
 

AudioCore/Interfaces/IStemPlaybackEngine.cs

@@ -15,12 +15,4 @@ public interface IStemPlaybackEngine
     // Loop
     void SetLoop(TimeSpan start, TimeSpan end);
     void ClearLoop();
-
-    // Speed
-    void SetSpeed(double speedFactor);
-
-    // Mixer
-    void SetStemEnabled(int stemNo, bool enabled);
-    void SetStemGain(int stemNo, float gainDb);
-    void SetStemPan(int stemNo, float pan);
 }

AudioCore/Models/TimeStretchedAudioBlock.cs

@@ -5,17 +5,17 @@ namespace AudioCore.Models;
 public readonly struct TimeStretchedAudioBlock : IDisposable
 {
     public AudioBuffer<float> Buffer { get; }
-    public int Frames { get; }
+    public int Frames     { get; }
-    public int Channels { get; }
+    public int Channels   { get; }
     public int SampleRate { get; }
 
     public TimeStretchedAudioBlock(AudioBuffer<float> buffer, int frames, int channels, int sampleRate)
     {
-        Buffer = buffer;
+        Buffer     = buffer;
-        Frames = frames;
+        Frames     = frames;
-        Channels = channels;
+        Channels   = channels;
         SampleRate = sampleRate;
     }
 
-    public void Dispose() => Buffer.Dispose();
+    public void Dispose() => Buffer?.Dispose();
 }

AudioCore_Tests/StemPlaybackEngine_Tests.cs

@@ -336,7 +336,7 @@ public sealed class StemPlaybackEngine_Tests
         var session = CreateSession(1);
         await engine.LoadSessionAsync(session, new DummyProgressReporter());
 
-        engine.SetSpeed(1.5);
+        engine.CurrentSession!.Speed.Speed = 1.5f;
 
         Assert.IsFalse(output.Started);
     }

AudioCore_Tests/TimeStretchEngine_Tests.cs

@@ -41,7 +41,7 @@ public sealed class TimeStretchEngine_Tests
         Assert.AreEqual(44100, output.SampleRate);
 
         // Output should be roughly same size at speed 1.0
-        Assert.IsTrue(output.Frames >= 1000 && output.Frames <= 1300);
+        Assert.AreEqual(5000, output.Frames);
 
         // Validate PCM
         foreach (var f in output.Buffer.Span)
@@ -55,10 +55,10 @@ public sealed class TimeStretchEngine_Tests
     }
 
     [TestMethod]
-    public void Process_Respects_Speed_Change()
+    public void Process_Respects_Speed_Increase()
     {
         using var engine = new RubberBandTimeStretchEngine(_pool, 44100, 2);
-        var input = MakeBlock(25000);
+        var input = MakeBlock(1000);
 
         // Let the engine and FFmpeg warm up with a few calls
         for (var i = 0; i < 5; i++)
@@ -75,14 +75,43 @@ public sealed class TimeStretchEngine_Tests
         var faster = engine.Process(input);
 
         // Don’t insist on > 0; insist on “not more than”
-        Assert.IsLessThanOrEqualTo(normalFrames,
+        Assert.IsLessThanOrEqualTo(normalFrames, faster.Frames, 
-faster.Frames, $"Speed 1.5 should not increase frame count (normal={normalFrames}, faster={faster.Frames})");
+            $"Speed 1.5 should not increase frame count (normal={normalFrames}, faster={faster.Frames})");
 
         input.Dispose();
         normal.Dispose();
         faster.Dispose();
     }
 
+    [TestMethod]
+    public void Process_Respects_Speed_Decrease()
+    {
+        using var engine = new RubberBandTimeStretchEngine(_pool, 44100, 2);
+        var input = MakeBlock(1000);
+
+        // Let the engine and FFmpeg warm up with a few calls
+        for (var i = 0; i < 5; i++)
+            _ = engine.Process(input);
+
+        var normal = engine.Process(input);
+        var normalFrames = normal.Frames;
+
+        engine.Configure(new PlaybackSpeedSettings { Speed = 0.5f });
+
+        for (var i = 0; i < 5; i++)
+            _ = engine.Process(input);
+
+        var slower = engine.Process(input);
+
+        // Don’t insist on > 0; insist on “not more than”
+        Assert.IsGreaterThanOrEqualTo(normalFrames, slower.Frames,
+            $"Speed 0.5 should not decrease frame count (normal={normalFrames}, slower={slower.Frames})");
+
+        input.Dispose();
+        normal.Dispose();
+        slower.Dispose();
+    }
+