unclshura/ABStemPlayer
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Correct(-ish) position displayed when sppeding up or slowing dowm audio

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This commit is contained in:
Alexander Shabarshov 2026-08-15 10:02:46 +01:00
parent 4c8d4d2ed9
commit 46ed183e3f
4 changed files with 134 additions and 64 deletions
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2
ABStemPlayer/ViewModels/WaveformBandViewModel.cs
View File

@ -47,7 +47,7 @@ public partial class WaveformBandViewModel : ObservableObject
return;
}
double ratio = current.TotalSeconds / total.TotalSeconds;
double ratio = current.TotalMicroseconds / total.TotalMicroseconds;
PlaybackX = ratio * CanvasWidth;
}

8
AudioCore/AudioCore.csproj
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@ -3,9 +3,7 @@
<PropertyGroup>
<IsPackable>true</IsPackable>
<Authors>Alexander Shabarshov</Authors>
<Description>
Audio engine core for ABStemPlayer. Audio pipeline.
</Description>
<Description>Audio engine core for ABStemPlayer. Audio pipeline. </Description>
<PackageProjectUrl>https://github.com/unclshura/ABStemPlayer</PackageProjectUrl>
<PackageTags>audio, player, ab, guitar, drums, piano, stem, mixer, c#</PackageTags>
<PackageReadmeFile>README.md</PackageReadmeFile>
@ -34,8 +32,8 @@
<PropertyGroup>
<Version>1.0.0</Version>
<BuildNumber>0</BuildNumber>
<SourceRevisionId>0000</SourceRevisionId>
<InformationalVersion>$(Version).$(BuildNumber)+$(SourceRevisionId)</InformationalVersion>
<SourceRevisionId></SourceRevisionId>
<InformationalVersion>$(Version).$(BuildNumber)$(SourceRevisionId)</InformationalVersion>
<AssemblyVersion>$(Version)</AssemblyVersion>
<FileVersion>$(Version).$(BuildNumber)</FileVersion>
</PropertyGroup>

115
AudioCore/Impl/RubberBandTimeStretchEngine.cs
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@ -10,6 +10,15 @@ public sealed class RubberBandTimeStretchEngine : ITimeStretchEngine, IAsyncDisp
private readonly int _sampleRate;
private long[] _sourcePositions;
private sealed class SourceChunkInfo
{
public long SourcePosition; // starting frame index in source stream
public int SourceFrames; // number of frames in this chunk
}
private readonly Queue<SourceChunkInfo>[] _pendingInput;
private double[] _fractionalInput;
// One RubberBand/ffmpeg process per stem (each is stereo: 2 channels)
private sealed class StemProcess : IDisposable
{
@ -51,6 +60,12 @@ public sealed class RubberBandTimeStretchEngine : ITimeStretchEngine, IAsyncDisp
_stemProcesses.Capacity = stemCount;
_stemCount = stemCount;
_sourcePositions = new long[_stemCount];
_fractionalInput = new double[_stemCount];
_pendingInput = Enumerable.Range(0, _stemCount)
.Select(_ => new Queue<SourceChunkInfo>())
.ToArray();
}
public async Task Configure(PlaybackSpeedSettings settings, CancellationToken token)
@ -78,29 +93,45 @@ public sealed class RubberBandTimeStretchEngine : ITimeStretchEngine, IAsyncDisp
if (stemBlocks.Count != _stemCount)
throw new ArgumentException($"Expected {_stemCount} stems, but got {stemBlocks.Count}.");
EnsureStemProcesses(stemBlocks.Count);
// No-stretch path: just enqueue into per-stem rings
if (Math.Abs(_speed - 1.0f) < 0.01f)
{
EnsureStemProcesses(stemBlocks.Count);
for (int i = 0; i < stemBlocks.Count; i++)
{
var proc = _stemProcesses[i];
var bytes = MemoryMarshal.AsBytes(stemBlocks[i].Buffer.Span);
proc.Ring.Write(bytes, bytes.Length, token);
var block = stemBlocks[i];
// Track source position for passthrough mode
_pendingInput[i].Enqueue(new SourceChunkInfo
{
SourcePosition = block.Position,
SourceFrames = block.Frames
});
var bytes = MemoryMarshal.AsBytes(block.Buffer.Span);
_stemProcesses[i].Ring.Write(bytes, bytes.Length, token);
}
return Task.CompletedTask;
}
// Stretch path: one ffmpeg+rubberband per stem
EnsureStemProcesses(stemBlocks.Count);
StartProcessesIfNeeded(stemBlocks.Count);
for (int i = 0; i < stemBlocks.Count; i++)
{
var block = stemBlocks[i];
// Track source position for stretched mode
_pendingInput[i].Enqueue(new SourceChunkInfo
{
SourcePosition = block.Position,
SourceFrames = block.Frames
});
var proc = _stemProcesses[i];
var span = stemBlocks[i].Buffer.Span;
var span = block.Buffer.Span;
var bytes = MemoryMarshal.AsBytes(span);
try
@ -108,29 +139,31 @@ public sealed class RubberBandTimeStretchEngine : ITimeStretchEngine, IAsyncDisp
if (token.IsCancellationRequested)
return Task.CompletedTask;
// Only write if ffmpeg is alive
if (proc.Stdin != null && !(proc.Ff?.Proc?.HasExited ?? true))
{
proc.Stdin.Write(bytes);
if (token.IsCancellationRequested)
return Task.CompletedTask;
try
{
proc.Stdin?.Flush();
proc.Stdin.Flush();
}
catch (System.ObjectDisposedException)
catch (ObjectDisposedException)
{
// process has exited
// ffmpeg exited early
}
}
}
catch
{
// ignore
// Ignore write errors (ffmpeg may exit early)
}
}
return Task.CompletedTask;
}
public async Task<TimeStretchedAudioBlock[]> ReceiveStems(CancellationToken token)
{
EnsureStemProcesses(_stemCount);
@ -195,10 +228,10 @@ public sealed class RubberBandTimeStretchEngine : ITimeStretchEngine, IAsyncDisp
var outBytes = MemoryMarshal.AsBytes(outBuf.Span);
temp.AsSpan().CopyTo(outBytes);
// Compute source position
long sourceFrames = (long)(framesToRead * _speed);
long sourcePos = _sourcePositions[i];
_sourcePositions[i] += sourceFrames;
//
// *** Correct source-position mapping ***
//
long sourcePos = ComputeSourcePosition(i, framesToRead);
result[i] = new TimeStretchedAudioBlock(
outBuf,
@ -211,6 +244,54 @@ public sealed class RubberBandTimeStretchEngine : ITimeStretchEngine, IAsyncDisp
return result;
}
private long ComputeSourcePosition(int stemIndex, int outputFrames)
{
// inputFrames = outputFrames / speed
double neededInputFrames = outputFrames / _speed;
// Add fractional requirement
_fractionalInput[stemIndex] += neededInputFrames;
long sourcePos = 0;
bool first = true;
var queue = _pendingInput[stemIndex];
// If no input chunks exist (warm-up), return last known position
if (queue.Count == 0)
return _sourcePositions[stemIndex];
while (_fractionalInput[stemIndex] >= 1 && queue.Count > 0)
{
var chunk = queue.Peek();
int take = (int)Math.Min(chunk.SourceFrames, Math.Floor(_fractionalInput[stemIndex]));
if (take <= 0)
break;
if (first)
{
sourcePos = chunk.SourcePosition;
first = false;
}
chunk.SourceFrames -= take;
_fractionalInput[stemIndex] -= take;
if (chunk.SourceFrames == 0)
queue.Dequeue();
}
// If we consumed nothing (fraction < 1), use last known position
if (first)
sourcePos = _sourcePositions[stemIndex];
_sourcePositions[stemIndex] = sourcePos;
return sourcePos;
}
private void EnsureStemProcesses(int stemCount)
{

49
AudioCore/Impl/StemPlaybackEngine.cs
View File

@ -39,7 +39,6 @@ public sealed class StemPlaybackEngine : IStemPlaybackEngine, IDisposable
private LoopRegion _loopRegion = new();
private long _decodedFramePosition;
private long _loopStartFrames;
private long _loopEndFrames;
@ -96,7 +95,6 @@ public sealed class StemPlaybackEngine : IStemPlaybackEngine, IDisposable
}
_pendingSeekFrames = 0;
_decodedFramePosition = 0;
}
}
@ -126,7 +124,6 @@ public sealed class StemPlaybackEngine : IStemPlaybackEngine, IDisposable
d.Seek(_pendingSeekFrames);
}
_decodedFramePosition = _pendingSeekFrames;
}
_pipeline.RenderTask = Task.Run(() => RenderLoopAsync(_pipeline, _pipeline.Cts.Token));
@ -163,7 +160,6 @@ public sealed class StemPlaybackEngine : IStemPlaybackEngine, IDisposable
if (!IsPlaying && _pipeline is null)
return;
_decodedFramePosition = 0;
_pendingSeekFrames = 0;
pipelineToDispose = _pipeline;
@ -201,12 +197,6 @@ public sealed class StemPlaybackEngine : IStemPlaybackEngine, IDisposable
{
foreach (var d in _pipeline.Decoders)
d.Seek(frameIndex);
_decodedFramePosition = frameIndex;
}
else
{
_decodedFramePosition = frameIndex;
}
}
@ -349,15 +339,9 @@ public sealed class StemPlaybackEngine : IStemPlaybackEngine, IDisposable
try { d.Seek(loopStart); } catch { }
}
lock (_stateLock)
_decodedFramePosition = loopStart;
// continue decoding from the loop start
continue;
}
lock (_stateLock)
_decodedFramePosition = nextPosition;
}
}
catch { }
@ -430,19 +414,7 @@ public sealed class StemPlaybackEngine : IStemPlaybackEngine, IDisposable
_outputDevice.Write(mixed.Buffer.Span);
gotFirstBlock = true;
try
{
double progress;
lock (_stateLock)
{
var total = _session?.StemSet.TotalFrames ?? 1L;
progress = (double)mixed.Position / Math.Max(total, 1L);
}
if (_progressReporter != null)
await _progressReporter.ReportProgress(progress).ConfigureAwait(false);
}
catch { }
await ReportProgress(mixed).ConfigureAwait(false);
try { mixed.Dispose(); } catch { }
foreach (var b in stretchedBlocks)
@ -459,6 +431,25 @@ public sealed class StemPlaybackEngine : IStemPlaybackEngine, IDisposable
}
}
private async Task ReportProgress(MixedAudioBlock mixed)
{
if (_progressReporter == null)
return;
try
{
double progress;
lock (_stateLock)
{
var total = _session?.StemSet.TotalFrames ?? 1L;
progress = (double)mixed.Position / Math.Max(total, 1L);
}
await _progressReporter.ReportProgress(progress).ConfigureAwait(false);
}
catch { }
}
private long TimeToFrames(TimeSpan time)
{
return (long)(time.TotalSeconds * _outputDevice.SampleRate);