Speed change on the fly is almost working. Still hangs sometime.

ABStemPlayer/ViewModels/MixerViewModel.cs

@@ -4,7 +4,7 @@ namespace ABStemPlayer.ViewModels;
 
 public sealed class MixerViewModel
 {
-    public ObservableCollection<StemChannelViewModel> Stems { get; } = new();
+    public ObservableCollection<StemChannelViewModel> Stems { get; } = [];
 
     public MixerViewModel()
     {

ABStemPlayer/ViewModels/PlaybackViewModel.cs

@@ -54,8 +54,8 @@ public sealed partial class PlaybackViewModel : ObservableObject
     [ObservableProperty] private TimeSpan       _totalTime;
     [ObservableProperty] private MixerViewModel _mixer = null!;
 
-    public ObservableCollection<SegmentViewModel>      Segments { get; } = new();
+    public ObservableCollection<SegmentViewModel>      Segments { get; } = [];
-    public ObservableCollection<WaveformBandViewModel> Bands    { get; } = new();
+    public ObservableCollection<WaveformBandViewModel> Bands    { get; } = [];
     
 
     private TimeSpan? _loopA;

ABStemPlayer/ViewModels/WaveformBandViewModel.cs

@@ -25,11 +25,11 @@ public partial class WaveformBandViewModel : ObservableObject
     [ObservableProperty] private double _canvasHeight;
     [ObservableProperty] private Geometry? _waveformGeometry;
 
-    public ObservableCollection<WaveformBar> WaveformBars { get; } = new();
+    public ObservableCollection<WaveformBar> WaveformBars { get; } = [];
 
     [ObservableProperty] private double _playbackX;
 
-    public ObservableCollection<SegmentViewModel> Segments { get; } = new();
+    public ObservableCollection<SegmentViewModel> Segments { get; } = [];
 
     public TimeSpan Duration { get; set; }
     public string DurationFormatted => Duration.ToString("mm\\:ss");

AudioCore/Impl/AudioBuffer.cs

@@ -1,8 +1,11 @@
+using System.Runtime.InteropServices;
+
 namespace AudioCore.Impl;
 
-public class AudioBuffer<T> : IDisposable
+public class AudioBuffer<T> : IDisposable where T : unmanaged
 {
     private readonly GenericBufferPool<T> _owner;
+    private static GenericBufferPool<byte> _bytePool = new GenericBufferPool<byte>();
     private bool _disposed;
 
     public T[] Samples { get; }
@@ -24,4 +27,19 @@ public class AudioBuffer<T> : IDisposable
         _owner.Return(Samples);
         _disposed = true;
     }
+
+    public async Task WriteAsync(Stream stream, CancellationToken token)
+    {
+        using var outBuf = _bytePool.Rent(Samples.Length * sizeof(T));
+
+        var src = Samples.AsSpan(0, Length);
+        var dst = outBuf.Span;
+
+        MemoryMarshal.Cast<T, byte>(src).CopyTo(dst);
+
+        await stream.WriteAsync(outBuf.Samples, 0, dst.Length, token)
+                    .ConfigureAwait(false);
+    }
+
+
 }

AudioCore/Impl/FfmpegProcess.cs

@@ -1,6 +1,7 @@
 using System.Buffers;
 using System.Diagnostics;
 using System.Runtime.InteropServices;
+using static AudioCore.Models.Tracer;
 
 namespace AudioCore.Impl;
 
@@ -27,7 +28,7 @@ public sealed class FfmpegProcess : IDisposable
 
     public void StartProcess()
     {
-        Debug.WriteLine($"{_name}: Starting ffmpeg process: {_commandLine.Replace("\r", "").Replace("\n", " ").Replace("\t", " ")}");
+        Msg($"{_name}: Starting ffmpeg process: {_commandLine.Replace("\r", "").Replace("\n", " ").Replace("\t", " ")}");
 
         var psi = new ProcessStartInfo
         {
@@ -119,7 +120,7 @@ public sealed class FfmpegProcess : IDisposable
     private void DisposeProcessOnly()
     {
         if (Proc != null)
-            Debug.WriteLine($"{_name}: Disposing ffmpeg process");
+            Msg($"{_name}: Disposing ffmpeg process");
 
         try { Stdout?.Dispose(); Stdout = null; } catch { }
         try { Stdin?.Dispose(); Stdin = null; } catch { }

AudioCore/Impl/GenericBufferPool.cs

@@ -2,7 +2,7 @@ using System.Buffers;
 
 namespace AudioCore.Impl;
 
-public class GenericBufferPool<T>
+public class GenericBufferPool<T> where T : unmanaged
 {
     private readonly ArrayPool<T> _pool = ArrayPool<T>.Shared;
 

AudioCore/Impl/RubberBandTimeStretchEngine.cs

@@ -1,5 +1,4 @@
-using System.Diagnostics;
+using System.Runtime.InteropServices;
-using System.Runtime.InteropServices;
 using static AudioCore.Models.Tracer;
 
 namespace AudioCore.Impl;
@@ -8,7 +7,7 @@ public sealed class RubberBandTimeStretchEngine : ITimeStretchEngine, IAsyncDisp
 {
     private readonly AudioBufferPool _pool;
     private readonly int             _sampleRate;
-    private long[] _sourcePositions;
+    private readonly long[]          _sourcePositions;
 
     private sealed class SourceChunkInfo
     {
@@ -17,7 +16,14 @@ public sealed class RubberBandTimeStretchEngine : ITimeStretchEngine, IAsyncDisp
     }
 
     private readonly Queue<SourceChunkInfo>[] _pendingInput;
-    private double[] _fractionalInput;
+    private readonly double[]                 _fractionalInput;
+    private readonly List<StemProcess>        _stemProcesses = [];
+    private readonly int                      _stemCount;
+    private int                               _activeIo; // Interlocked counter
+    private float                             _speed = 1.0f;
+    private CancellationTokenSource?          _cts;
+    private CancellationToken                 _token;
+    private Task?                             _readerTask;
 
     // One RubberBand/ffmpeg process per stem (each is stereo: 2 channels)
     private sealed class StemProcess : IDisposable
@@ -45,13 +51,7 @@ public sealed class RubberBandTimeStretchEngine : ITimeStretchEngine, IAsyncDisp
         }
     }
 
-    private readonly List<StemProcess> _stemProcesses = new();
-    private readonly int _stemCount;
 
-    private float                    _speed = 1.0f;
-    private CancellationTokenSource? _cts;
-    private CancellationToken        _token;
-    private Task?                    _readerTask;
 
     public RubberBandTimeStretchEngine(AudioBufferPool pool, int sampleRate = 44100, int stemCount = 6)
     {
@@ -62,22 +62,24 @@ public sealed class RubberBandTimeStretchEngine : ITimeStretchEngine, IAsyncDisp
         _sourcePositions        = new long[_stemCount];
         _fractionalInput        = new double[_stemCount];
 
-        _pendingInput = Enumerable.Range(0, _stemCount)
+        _pendingInput = [.. Enumerable.Range(0, _stemCount).Select(_ => new Queue<SourceChunkInfo>())];
-            .Select(_ => new Queue<SourceChunkInfo>())
-            .ToArray();
-
     }
 
-    public async Task Configure(PlaybackSpeedSettings settings, CancellationToken token)
+    public async Task Configure(PlaybackSpeedSettings settings, CancellationToken globalToken)
     {
         Trace(settings);
+
+        var speedChanged = Math.Abs(_speed - settings.Speed) > 0.01f;
+
         _speed = settings.Speed;
 
-        if (_cts != null)
+        if (globalToken != CancellationToken.None)
-            await DisposeProcesses().ConfigureAwait(false);
+            _token = globalToken;
 
-        if ( token != CancellationToken.None )
+        if (_cts != null && speedChanged)
-            _token = token;
+        {
+            await DisposeProcesses().ConfigureAwait(false);
+        }
     }
 
 
@@ -88,7 +90,10 @@ public sealed class RubberBandTimeStretchEngine : ITimeStretchEngine, IAsyncDisp
         return Task.CompletedTask;
     }
 
-    public Task SubmitStems(IReadOnlyList<AudioBlock> stemBlocks, CancellationToken token)
+    public async Task SubmitStems(IReadOnlyList<AudioBlock> stemBlocks, CancellationToken token)
+    {
+        Interlocked.Increment(ref _activeIo);
+        try
         {
             if (stemBlocks.Count != _stemCount)
             throw new ArgumentException($"Expected {_stemCount} stems, but got {stemBlocks.Count}.");
@@ -100,6 +105,9 @@ public sealed class RubberBandTimeStretchEngine : ITimeStretchEngine, IAsyncDisp
             {
                 for (int i = 0; i < stemBlocks.Count; i++)
                 {
+                    if (token.IsCancellationRequested)
+                        return;
+
                     var block = stemBlocks[i];
 
                     // Track source position for passthrough mode
@@ -113,7 +121,7 @@ public sealed class RubberBandTimeStretchEngine : ITimeStretchEngine, IAsyncDisp
                     _stemProcesses[i].Ring.Write(bytes, bytes.Length, token);
                 }
 
-            return Task.CompletedTask;
+                return;
             }
 
             // Stretch path: one ffmpeg+rubberband per stem
@@ -131,22 +139,20 @@ public sealed class RubberBandTimeStretchEngine : ITimeStretchEngine, IAsyncDisp
                 });
 
                 var proc  = _stemProcesses[i];
-            var span  = block.Buffer.Span;
-            var bytes = MemoryMarshal.AsBytes(span);
 
                 try
                 {
                     if (token.IsCancellationRequested)
-                    return Task.CompletedTask;
+                        return;
 
                     // Only write if ffmpeg is alive
                     if (proc.Stdin != null && !(proc.Ff?.Proc?.HasExited ?? true))
                     {
-                    proc.Stdin.Write(bytes);
+                        await block.Buffer.WriteAsync(proc.Stdin, token).ConfigureAwait(false);
 
                         try
                         {
-                        proc.Stdin.Flush();
+                            await proc.Stdin.FlushAsync(token).ConfigureAwait(false);
                         }
                         catch (ObjectDisposedException)
                         {
@@ -154,17 +160,27 @@ public sealed class RubberBandTimeStretchEngine : ITimeStretchEngine, IAsyncDisp
                         }
                     }
                 }
+                catch (TaskCanceledException)
+                {
+                    break;
+                }
                 catch
                 {
                     // Ignore write errors (ffmpeg may exit early)
                 }
             }
-
+        }
-        return Task.CompletedTask;
+        finally
+        {
+            Interlocked.Decrement(ref _activeIo);
+        }
     }
 
 
     public async Task<TimeStretchedAudioBlock[]> ReceiveStems(CancellationToken token)
+    {
+        Interlocked.Increment(ref _activeIo);
+        try
         {
             EnsureStemProcesses(_stemCount);
 
@@ -190,7 +206,7 @@ public sealed class RubberBandTimeStretchEngine : ITimeStretchEngine, IAsyncDisp
                 }
 
                 if (token.IsCancellationRequested)
-                return Array.Empty<TimeStretchedAudioBlock>();
+                    return [];
 
                 // Determine block size (final block may be smaller)
                 int bytesToRead    = Math.Min(bytesPerBlock, available);
@@ -218,7 +234,7 @@ public sealed class RubberBandTimeStretchEngine : ITimeStretchEngine, IAsyncDisp
                 }
 
                 if (token.IsCancellationRequested)
-                return Array.Empty<TimeStretchedAudioBlock>();
+                    return [];
 
                 // Now allocate the float buffer
                 var outBuf = _pool.Rent(samplesToRead);
@@ -243,6 +259,11 @@ public sealed class RubberBandTimeStretchEngine : ITimeStretchEngine, IAsyncDisp
 
             return result;
         }
+        finally
+        {
+            Interlocked.Decrement(ref _activeIo);
+        }
+    }
 
 private long ComputeSourcePosition(int stemIndex, int outputFrames)
     {
@@ -341,37 +362,37 @@ private long ComputeSourcePosition(int stemIndex, int outputFrames)
 
         var buf = new byte[4096];
 
-        try
-        {
         while (!token.IsCancellationRequested)
         {
-                bool anyActive = false;
+            try
-
+            {
                 foreach (var proc in _stemProcesses)
                 {
                     if (proc.Stdout == null)
                         continue;
 
-                    anyActive = true;
+                    var read = await proc.Stdout.ReadAsync(buf, token).ConfigureAwait(false);
-
-                    var read = await proc.Stdout.ReadAsync(buf, 0, buf.Length, token).ConfigureAwait(false);
                     if (read > 0)
                         proc.Ring.Write(buf, read, token);
                 }
-
-                if (!anyActive)
-                    break;
             }
+            catch (OperationCanceledException)
+            {
+                // expected on dispose; let outer while exit via token
+                return;
             }
             catch { }
         }
+    }
 
     private async Task DisposeProcesses()
     {
+        Trace();
+
         if (_cts != null)
         {
             Msg("Cancelling RubberBand/ffmpeg reader task...");
-            try { _cts.Cancel(); } catch { }
+            try { await _cts.CancelAsync(); } catch { }
         }
 
         if (_readerTask != null)
@@ -390,16 +411,29 @@ private long ComputeSourcePosition(int stemIndex, int outputFrames)
             _stemProcesses.Clear();
         }
 
-        if (_cts != null)
+        _cts?.Dispose();
-        {
-            _cts.Dispose();
         _cts = null;
+
+        // Reset position tracking
+        for (int i = 0; i < _stemCount; i++)
+        {
+            _pendingInput[i].Clear();
+            _fractionalInput[i] = 0;
+            _sourcePositions[i] = 0;
         }
+
+        _readerTask = null;
+
+        _cts = null;
+
+        // Wait until no active I/O before tearing down
+        while (Interlocked.CompareExchange(ref _activeIo, 0, 0) != 0)
+            await Task.Delay(1, CancellationToken.None).ConfigureAwait(false);
+
     }
 
     public async ValueTask DisposeAsync()
     {
-        Trace();
         await DisposeProcesses().ConfigureAwait(false);
     }
 }

AudioCore/Impl/StemPlaybackEngine.cs

@@ -48,6 +48,9 @@ public sealed class StemPlaybackEngine : IStemPlaybackEngine, IDisposable
     private PipelineState?               _pipeline;
     private long                         _pendingSeekFrames;
 
+    private PlaybackSpeedSettings _currentSpeed = new(){ Speed = 1.0f };
+    private PlaybackSpeedSettings _prevSpeed    = new(){ Speed = 1.0f };
+
     public StemPlaybackEngine(
         IStemDecoderFactory stemDecoderFactory,
         IAudioOutputDevice outputDevice,
@@ -168,7 +171,10 @@ public sealed class StemPlaybackEngine : IStemPlaybackEngine, IDisposable
 
         if (pipelineToDispose is not null)
         {
-            try { pipelineToDispose.Cts?.Cancel(); } catch { }
+            if (pipelineToDispose.Cts != null)
+            {
+                try { await pipelineToDispose.Cts.CancelAsync(); } catch { }
+            }
 
             var task = pipelineToDispose.RenderTask;
             if (task is not null && task.Id != Task.CurrentId)
@@ -207,7 +213,7 @@ public sealed class StemPlaybackEngine : IStemPlaybackEngine, IDisposable
     {
         Trace(settings);
 
-        await _timeStretchEngine.Configure(settings, _pipeline?.Cts?.Token ?? CancellationToken.None).ConfigureAwait(false);
+        _currentSpeed = settings;
     }
 
     public Task UpdateMixerAsync(MixerSettings settings)
@@ -392,6 +398,12 @@ public sealed class StemPlaybackEngine : IStemPlaybackEngine, IDisposable
             var gotFirstBlock = false;
             while (!token.IsCancellationRequested)
             {
+                if ( _prevSpeed.Speed != _currentSpeed.Speed )
+                {
+                    await _timeStretchEngine.Configure(_currentSpeed, token).ConfigureAwait(false);
+                    _prevSpeed = _currentSpeed;
+                }
+
                 var stretchedBlocks = await _timeStretchEngine.ReceiveStems(token).ConfigureAwait(false);
 
                 if (stretchedBlocks == null || stretchedBlocks.Length == 0 || stretchedBlocks[0].Buffer == null)

AudioCore/Impl/WasapiOutputDevice.cs

@@ -3,6 +3,7 @@ using System.Runtime.InteropServices;
 using NAudio.CoreAudioApi;
 using NAudio.Dmo;
 using NAudio.Wave;
+using static AudioCore.Models.Tracer;
 
 namespace AudioCore.Impl;
 

AudioCore/Interfaces/ITimeStretchEngine.cs

@@ -10,7 +10,7 @@ public sealed class PlaybackSpeedSettings
 
 public interface ITimeStretchEngine
 {
-    Task Configure(PlaybackSpeedSettings settings, CancellationToken token);
+    Task Configure(PlaybackSpeedSettings settings, CancellationToken globalToken = default);
 
     // Streaming block processing
     Task IsReadyToAcceptStems(CancellationToken token);

AudioCore/Models/Tracer.cs

@@ -8,15 +8,12 @@ namespace AudioCore.Models;
 
 public static class Tracer
 {
-    public static void Trace([CallerMemberName] string method = null!) => Debug.WriteLine($"TRACE: ____________ {method}() called");
+    public static void Trace([CallerFilePath] string path = null!, [CallerMemberName] string method = null!) 
-    public static void Trace<T>(T args, [CallerArgumentExpression("args")] string argsExpression = "", [CallerMemberName] string method = "")
+        => Debug.WriteLine($"TRACE: ____________ {Path.GetFileNameWithoutExtension(path)}.{method}() called");
-    {
+    public static void Trace<T>(T args, [CallerArgumentExpression("args")] string argsExpression = "", [CallerFilePath] string path = null!, [CallerMemberName] string method = "")
-        Debug.WriteLine($"TRACE: ____________ {method}({argsExpression}: {args}) called");
+        => Debug.WriteLine($"TRACE: ____________ {Path.GetFileNameWithoutExtension(path)}.{method}({argsExpression}: {args}) called");
-    }
+    public static void Trace<T1, T2>(T1 arg1, T2 arg2, [CallerArgumentExpression("arg1")] string arg1Expression = "", [CallerArgumentExpression("arg2")] string arg2Expression = "", [CallerFilePath] string path = null!, [CallerMemberName] string method = "")
-    public static void Trace<T1, T2>(T1 arg1, T2 arg2, [CallerArgumentExpression("arg1")] string arg1Expression = "", [CallerArgumentExpression("arg2")] string arg2Expression = "", [CallerMemberName] string method = "")
+        => Debug.WriteLine($"TRACE: ____________ {Path.GetFileNameWithoutExtension(path)}.{method}({arg1Expression}: {arg1}, {arg2Expression}: {arg2}) called");
-    {
+    public static void Msg(string message, [CallerFilePath] string path = null!, [CallerMemberName] string method = null!)
-        Debug.WriteLine($"TRACE: ____________ {method}({arg1Expression}: {arg1}, {arg2Expression}: {arg2}) called");
+        => Debug.WriteLine($"TRACE: ____________ {Path.GetFileNameWithoutExtension(path)}.{method}(): {message}");
-    }
-
-    public static void Msg(string message, [CallerMemberName] string method = null!) => Debug.WriteLine($"TRACE: ____________ {method}(): {message}");
 }