Multi-track + shaped/raw recording (per-peer split tracks) — held for next release

Recording Settings gains two per-profile toggles (Ed's request):
 * "Split recording into separate tracks" — each recording becomes a folder with one file per
   connected peer (their received audio only) plus one for your own send.
 * "Bypass pan and EQ when recording" — record the RAW audio (before pan/EQ) instead of the
   shaped audio you hear; applies to single and split.

Engine: a per-peer record tap in SessionPlayout hands each peer's block to the recorder RAW
(before pan/EQ) or SHAPED (after) per the bypass flag; PlayoutEngine propagates the tap to all
sessions (+ inherits on reconnect) and fires OnRecordBlockComplete each render; AudioReceiver
exposes SetPeerRecordTap / OnRecordBlockComplete. AudioRecorder now accepts an explicit path and
exposes ExtensionFor. RecordingController composes one AudioRecorder per track: multi-track =
a recorder per connected peer + a "me" recorder; single-track shaped = the existing mixed tap;
single-track raw (bypass) = sum each peer's raw block per render, flushed on the block boundary.

Naming (Ed's scheme, sortable): <recordings>/<yyyy-MM-dd>/ then, single-track, "<HH-mm-ss>
RemSound recording.<ext>"; multi-track, a folder "<HH-mm-ss> RemSound recording multi track/"
containing "<machine name> <HH-mm-ss>.<ext>" per peer (name or IP) and for your own send.

Known edge (noted): a peer using sender-side BothIndependent (two lanes) records both lanes to
one file in a split recording; single-track bypass sums per render in the Mixed path. Off by
default (both toggles unticked = today's behaviour). Builds clean; pending Ed's hands-on test.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/RemSound.App/AudioRecorder.cs

@@ -135,19 +135,29 @@ internal sealed class AudioRecorder : IDisposable
     /// <summary>Constructs the recorder, opens the output file, and starts the writer
     /// thread. If anything fails the constructor throws and no cleanup is needed (no
     /// file has been opened yet).</summary>
-    public AudioRecorder(RecordingSettings settings, Action<string>? onDiagnostic, Action<string, long>? onFinished)
+    public AudioRecorder(RecordingSettings settings, Action<string>? onDiagnostic, Action<string, long>? onFinished, string? explicitPath = null)
     {
         this.settings = settings.Clone();
         this.onDiagnostic = onDiagnostic;
         this.onFinished = onFinished;
 
-        var folder = settings.ResolvedFolder();
+        if (explicitPath is not null)
-        if (string.IsNullOrWhiteSpace(folder)) folder = RecordingSettings.DefaultFolder();
+        {
-        Directory.CreateDirectory(folder);
+            // The RecordingController drives the folder/file naming (date folders, per-peer split
+            // tracks). Honour the path it hands us, creating the containing folder.
+            resolvedPath = explicitPath;
+            Directory.CreateDirectory(Path.GetDirectoryName(explicitPath) ?? RecordingSettings.DefaultFolder());
+        }
+        else
+        {
+            var folder = settings.ResolvedFolder();
+            if (string.IsNullOrWhiteSpace(folder)) folder = RecordingSettings.DefaultFolder();
+            Directory.CreateDirectory(folder);
 
-        var ext = ExtensionFor(settings.FileFormat);
+            var ext = ExtensionFor(settings.FileFormat);
-        var stamp = DateTime.Now.ToString("yyyy-MM-dd_HH-mm-ss");
+            var stamp = DateTime.Now.ToString("yyyy-MM-dd_HH-mm-ss");
-        resolvedPath = Path.Combine(folder, $"RemSound-{stamp}.{ext}");
+            resolvedPath = Path.Combine(folder, $"RemSound-{stamp}.{ext}");
+        }
 
         // Writer creation happens on the constructor thread so any open errors are surfaced
         // synchronously to the caller.
@@ -565,7 +575,7 @@ internal sealed class AudioRecorder : IDisposable
     private float[] recvDirectionScratch = new float[DrainChunkFrames * MixChannels];
     private float[] monoScratch = new float[DrainChunkFrames];
 
-    private static string ExtensionFor(RecordingFileFormat format) => format switch
+    public static string ExtensionFor(RecordingFileFormat format) => format switch
     {
         RecordingFileFormat.Wav => "wav",
         RecordingFileFormat.Mp3 => "mp3",

src/RemSound.App/MainForm.cs

@@ -823,6 +823,11 @@ public sealed class MainForm : Form
             settings,
             msg => logFile.Event($"recorder: {msg}"));
         recordingController.RecordingStateChanged += UpdateStartStopRecordingMenuLabel;
+        // Supply the connected peers when a split recording starts, so it can make one track per peer.
+        recordingController.ConnectedPeersProvider = () =>
+            selectedPeerEndpoints
+                .Select(kv => (kv.Value.Address, selectedPeerLabels.GetValueOrDefault(kv.Key, kv.Value.Address.ToString())))
+                .ToList();
 
         // --- Set accessibility names ---
         // For these four controls the keyboard shortcut is included explicitly in both the

src/RemSound.App/RecordingController.cs

@@ -1,3 +1,4 @@
+using System.Net;
 using RemSound.Core;
 using RemSound.Receiver;
 using RemSound.Sender;
@@ -22,6 +23,18 @@ internal sealed class RecordingController
     private readonly RemSoundSettingsStore settings;
     private readonly Action<string> diagnostic;
     private AudioRecorder? active;
+    // Multi-track (split) state — one recorder per connected peer (keyed by address), plus one for your
+    // own send. Built entirely at Start and only replaced with null at Stop, so the audio-thread tap can
+    // read the dictionary with a plain volatile read.
+    private volatile Dictionary<string, AudioRecorder>? peerRecorders;
+    private AudioRecorder? meRecorder;
+    // Single-file BYPASS state — sum each peer's RAW block per render, flush on the block boundary.
+    private float[] rawMixAccum = new float[4096];
+    private int rawMixLen;
+
+    /// <summary>Supplies the currently-connected peers (address + display name) at the moment a split
+    /// recording starts, so one track file is created per peer. Set by MainForm.</summary>
+    public Func<IReadOnlyList<(IPAddress Address, string Name)>>? ConnectedPeersProvider { get; set; }
 
     public RecordingController(AudioSender sender, AudioReceiver receiver, RemSoundSettingsStore settings, Action<string> diagnostic)
     {
@@ -31,7 +44,7 @@ internal sealed class RecordingController
         this.diagnostic = diagnostic;
     }
 
-    public bool IsRecording => active is not null;
+    public bool IsRecording => active is not null || meRecorder is not null || peerRecorders is not null;
 
     /// <summary>UTC clock at which the current recording started, or null when nothing is
     /// recording. Captured by <see cref="Start"/> and cleared by <see cref="Stop"/>. Used
@@ -49,15 +62,18 @@ internal sealed class RecordingController
     /// while recording, but the guard is here for safety).</summary>
     public void Start()
     {
-        if (active is not null) return;
+        if (IsRecording) return;
         var s = settings.LoadRecordingSettings();
+        var now = DateTime.Now;
         try
         {
-            active = new AudioRecorder(s, diagnostic, OnRecorderFinished);
+            if (s.SplitTracks) StartMultiTrack(s, now);
+            else StartSingleTrack(s, now);
         }
         catch (Exception ex)
         {
             diagnostic($"recording: failed to start: {ex.GetType().Name}: {ex.Message}");
+            CleanUpAfterFailedStart();
             MessageBox.Show(
                 $"Could not start recording:\n\n{ex.Message}",
                 "RemSound — recording",
@@ -65,13 +81,7 @@ internal sealed class RecordingController
                 MessageBoxIcon.Warning);
             return;
         }
-
-        // Wire taps. Each tap is independent — the recorder's source-mode filter decides
-        // whether to actually write the samples.
-        sender.OnSentSamples = active.WriteSent;
-        receiver.OnReceivedSamples = active.WriteReceived;
         RecordingStartedUtc = DateTime.UtcNow;
-        diagnostic($"recording: started → {active.FilePath} (source={s.Source}, format={s.FileFormat}, channels={s.ChannelMode})");
         RecordingStateChanged?.Invoke(true);
     }
 
@@ -80,24 +90,27 @@ internal sealed class RecordingController
     /// so the user knows where the file landed.</summary>
     public void Stop()
     {
-        var recorder = active;
+        if (!IsRecording) return;
-        if (recorder is null) return;
 
-        // Unhook taps FIRST so no more audio gets queued during the drain.
+        // Unhook every tap FIRST so no more audio is queued during the drain.
         sender.OnSentSamples = null;
         receiver.OnReceivedSamples = null;
+        receiver.SetPeerRecordTap(null, false);
+        receiver.OnRecordBlockComplete = null;
 
+        var single = active;
+        var me = meRecorder;
+        var peers = peerRecorders;
         active = null;
+        meRecorder = null;
+        peerRecorders = null;
+        rawMixLen = 0;
         RecordingStartedUtc = null;
-        try
+
-        {
+        StopRecorder(single);
-            recorder.Stop();
+        StopRecorder(me);
-            recorder.Dispose();
+        if (peers is not null) foreach (var r in peers.Values) StopRecorder(r);
-        }
+
-        catch (Exception ex)
-        {
-            diagnostic($"recording: stop threw {ex.GetType().Name}: {ex.Message}");
-        }
         RecordingStateChanged?.Invoke(false);
     }
 
@@ -106,6 +119,134 @@ internal sealed class RecordingController
         diagnostic($"recording: finished → {path} ({bytes:N0} bytes)");
     }
 
+    private void StartSingleTrack(RecordingSettings s, DateTime now)
+    {
+        var path = SingleTrackPath(s, now);
+        active = new AudioRecorder(s, diagnostic, OnRecorderFinished, path);
+        sender.OnSentSamples = active.WriteSent;
+        if (s.BypassShaping)
+        {
+            // Raw single file: the mixed receive tap is POST pan/EQ, so instead sum each peer's RAW
+            // block per render and flush it to the one recorder on the block boundary.
+            rawMixLen = 0;
+            receiver.SetPeerRecordTap(OnRawMixTap, raw: true);
+            receiver.OnRecordBlockComplete = FlushRawMix;
+        }
+        else
+        {
+            receiver.OnReceivedSamples = active.WriteReceived;   // the shaped mix — what you hear
+        }
+        diagnostic($"recording: started → {path} (source={s.Source}, format={s.FileFormat}, bypass={s.BypassShaping})");
+    }
+
+    private void StartMultiTrack(RecordingSettings s, DateTime now)
+    {
+        var folder = MultiTrackFolder(s, now);
+        Directory.CreateDirectory(folder);
+        var ext = AudioRecorder.ExtensionFor(s.FileFormat);
+        var time = now.ToString("HH-mm-ss");
+
+        // One track per connected peer (their received audio only), created up front on the UI thread
+        // so the audio-thread tap never has to open a file. Peers that join mid-recording aren't added.
+        var recs = new Dictionary<string, AudioRecorder>();
+        var usedNames = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
+        var byAddr = new Dictionary<string, string>();
+        foreach (var (addr, name) in ConnectedPeersProvider?.Invoke() ?? []) byAddr[addr.ToString()] = name;
+        foreach (var (addrKey, name) in byAddr)
+        {
+            var baseName = Sanitize(string.IsNullOrWhiteSpace(name) ? addrKey : name);
+            var fileName = $"{baseName} {time}";
+            if (!usedNames.Add(fileName)) fileName = $"{baseName} ({addrKey}) {time}";
+            var path = Path.Combine(folder, $"{fileName}.{ext}");
+            recs[addrKey] = new AudioRecorder(WithSource(s, RecordingSource.ReceivedOnly), diagnostic, OnRecorderFinished, path);
+        }
+        peerRecorders = recs;
+        receiver.SetPeerRecordTap(OnPeerRecordBlock, raw: s.BypassShaping);
+
+        // Your own track — your sent audio.
+        var mePath = Path.Combine(folder, $"{Sanitize(Environment.MachineName)} {time}.{ext}");
+        meRecorder = new AudioRecorder(WithSource(s, RecordingSource.SentOnly), diagnostic, OnRecorderFinished, mePath);
+        sender.OnSentSamples = meRecorder.WriteSent;
+
+        diagnostic($"recording: started multi-track → {folder} ({recs.Count} peer track(s), format={s.FileFormat}, bypass={s.BypassShaping})");
+    }
+
+    // Audio thread. Route each peer's block to that peer's recorder. peerRecorders is fully built at
+    // Start and only replaced with null at Stop, so a plain volatile read is safe.
+    private void OnPeerRecordBlock(IPEndPoint peer, ReadOnlyMemory<float> block)
+    {
+        var recs = peerRecorders;
+        if (recs is not null && recs.TryGetValue(peer.Address.ToString(), out var rec))
+            rec.WriteReceived(block, RenderRoute.Mixed);
+    }
+
+    // Audio thread. Sum a peer's raw block into the per-render mix for a single-file bypass recording.
+    private void OnRawMixTap(IPEndPoint peer, ReadOnlyMemory<float> block)
+    {
+        var span = block.Span;
+        if (rawMixAccum.Length < span.Length) rawMixAccum = new float[span.Length];
+        for (int i = 0; i < span.Length; i++) rawMixAccum[i] += span[i];
+        rawMixLen = span.Length;
+    }
+
+    // Audio thread. Flush the summed raw mix for this render to the single recorder, then reset.
+    private void FlushRawMix()
+    {
+        var rec = active;
+        int n = rawMixLen;
+        if (rec is not null && n > 0) rec.WriteReceived(rawMixAccum.AsMemory(0, n), RenderRoute.Mixed);
+        if (n > 0) { Array.Clear(rawMixAccum, 0, n); rawMixLen = 0; }
+    }
+
+    private void StopRecorder(AudioRecorder? r)
+    {
+        if (r is null) return;
+        try { r.Stop(); r.Dispose(); }
+        catch (Exception ex) { diagnostic($"recording: stop threw {ex.GetType().Name}: {ex.Message}"); }
+    }
+
+    private void CleanUpAfterFailedStart()
+    {
+        sender.OnSentSamples = null;
+        receiver.OnReceivedSamples = null;
+        receiver.SetPeerRecordTap(null, false);
+        receiver.OnRecordBlockComplete = null;
+        StopRecorder(active); active = null;
+        StopRecorder(meRecorder); meRecorder = null;
+        if (peerRecorders is not null) { foreach (var r in peerRecorders.Values) StopRecorder(r); peerRecorders = null; }
+    }
+
+    private static string BaseFolder(RecordingSettings s)
+    {
+        var f = s.ResolvedFolder();
+        return string.IsNullOrWhiteSpace(f) ? RecordingSettings.DefaultFolder() : f;
+    }
+
+    private static string DateFolder(RecordingSettings s, DateTime now) =>
+        Path.Combine(BaseFolder(s), now.ToString("yyyy-MM-dd"));
+
+    private static string SingleTrackPath(RecordingSettings s, DateTime now) =>
+        Path.Combine(DateFolder(s, now), $"{now:HH-mm-ss} RemSound recording.{AudioRecorder.ExtensionFor(s.FileFormat)}");
+
+    private static string MultiTrackFolder(RecordingSettings s, DateTime now) =>
+        Path.Combine(DateFolder(s, now), $"{now:HH-mm-ss} RemSound recording multi track");
+
+    private static RecordingSettings WithSource(RecordingSettings s, RecordingSource src)
+    {
+        var c = s.Clone();
+        c.Source = src;
+        return c;
+    }
+
+    private static string Sanitize(string name)
+    {
+        var invalid = Path.GetInvalidFileNameChars();
+        var sb = new System.Text.StringBuilder(name.Length);
+        foreach (var ch in name) sb.Append(Array.IndexOf(invalid, ch) >= 0 ? '_' : ch);
+        var r = sb.ToString().Trim().TrimEnd('.').Trim();
+        return string.IsNullOrEmpty(r) ? "peer" : r;
+    }
+
     /// <summary>Open the currently-configured recordings folder in Windows Explorer.
     /// Creates the folder if it doesn't yet exist (a fresh install hasn't recorded
     /// anything, so the folder won't be there). Surfaces filesystem errors to the user

src/RemSound.App/RecordingSettingsDialog.cs

@@ -125,6 +125,19 @@ internal sealed class RecordingSettingsDialog : Form
     private Control? compressionColumn;
     private TableLayoutPanel? grid;
 
+    private readonly AccessibleCheckBox splitTracksBox = new()
+    {
+        Text = "Split recording into separate &tracks — one file per peer, plus your own (Alt+T)",
+        AccessibleName = "Split recording into separate tracks, one file per peer plus your own send",
+        AutoSize = true,
+    };
+    private readonly AccessibleCheckBox bypassShapingBox = new()
+    {
+        Text = "Bypass pan and EQ when recording — record the &raw audio (Alt+R)",
+        AccessibleName = "Bypass pan and EQ when recording, record the raw audio",
+        AutoSize = true,
+    };
+
     private readonly Button okButton = new()
     {
         Text = "&OK",
@@ -153,6 +166,11 @@ internal sealed class RecordingSettingsDialog : Form
     public RecordingSettingsDialog(RecordingSettings current)
     {
         working = current?.Clone() ?? new RecordingSettings();
+
+        splitTracksBox.Checked = working.SplitTracks;
+        splitTracksBox.CheckedChanged += (_, _) => working.SplitTracks = splitTracksBox.Checked;
+        bypassShapingBox.Checked = working.BypassShaping;
+        bypassShapingBox.CheckedChanged += (_, _) => working.BypassShaping = bypassShapingBox.Checked;
         var initialSnapshot = working.Clone();
 
         Text = "Recording settings";
@@ -267,6 +285,20 @@ internal sealed class RecordingSettingsDialog : Form
         Controls.Add(grid);
         Controls.Add(buttonRow);
 
+        // The two per-recording toggles sit across the top of the dialog. Added last so docking
+        // resolves them to the top strip, above the option columns.
+        var optionsRow = new FlowLayoutPanel
+        {
+            Dock = DockStyle.Top,
+            FlowDirection = FlowDirection.TopDown,
+            AutoSize = true,
+            WrapContents = false,
+            Padding = new Padding(12, 12, 12, 0),
+        };
+        optionsRow.Controls.Add(splitTracksBox);
+        optionsRow.Controls.Add(bypassShapingBox);
+        Controls.Add(optionsRow);
+
         AcceptButton = okButton;
         CancelButton = cancelButton;
 

src/RemSound.Core/RecordingTypes.cs

@@ -100,6 +100,16 @@ public sealed class RecordingSettings
     /// machine, the recorder falls back to the default and notes it in the diagnostics.</summary>
     public string? Folder { get; set; }
 
+    /// <summary>When true, a recording is written as a FOLDER of separate tracks instead of one mixed
+    /// file: one file per connected peer (only that peer's received audio) plus one file for your own
+    /// sent audio. Off by default. (Ed's multi-track request.)</summary>
+    public bool SplitTracks { get; set; }
+
+    /// <summary>When true, per-peer pan and EQ are BYPASSED for the recording — it captures the raw,
+    /// unshaped audio even though you still hear the shaped version live. When false (default), your
+    /// pan/EQ are baked into the recording (and on a split recording, into each peer's own track).</summary>
+    public bool BypassShaping { get; set; }
+
     public RecordingSettings Clone() => new()
     {
         Source = Source,
@@ -111,6 +121,8 @@ public sealed class RecordingSettings
         FlacBitsPerSample = FlacBitsPerSample,
         FlacCompressionLevel = FlacCompressionLevel,
         Folder = Folder,
+        SplitTracks = SplitTracks,
+        BypassShaping = BypassShaping,
     };
 
     /// <summary>Default folder path used when <see cref="Folder"/> is blank. Computed at

src/RemSound.Receiver/AudioReceiver.cs

@@ -198,6 +198,20 @@ public sealed class AudioReceiver : IDisposable
     public void SetPeerDsp(IPAddress address, PeerDspChain? chain) =>
         playoutEngine.SetPeerDsp(address, chain);
 
+    /// <summary>Sets (or clears with null) the split-recording tap on every current and future session,
+    /// so the recorder receives each peer's block separately. <paramref name="raw"/> = before pan/EQ
+    /// (bypass), else after. Called from the UI thread.</summary>
+    public void SetPeerRecordTap(Action<IPEndPoint, ReadOnlyMemory<float>>? tap, bool raw) =>
+        playoutEngine.SetRecordTap(tap, raw);
+
+    /// <summary>Fired once per rendered block, right after <see cref="OnReceivedSamples"/> — the block
+    /// boundary a single-file bypass recording uses to flush its per-peer sum.</summary>
+    public Action? OnRecordBlockComplete
+    {
+        get => playoutEngine.OnRecordBlockComplete;
+        set => playoutEngine.OnRecordBlockComplete = value;
+    }
+
     /// <summary>
     /// Optional callback invoked when the engine produces fully-processed mixed received
     /// audio (volume / mute / limiter all applied). Span is 48 kHz interleaved stereo

src/RemSound.Receiver/PlayoutEngine.cs

@@ -49,6 +49,10 @@ internal sealed class PlayoutEngine : IWaveProvider
     // peer's shaping from frame zero — the same "applies to future sessions too" idea as the
     // concealment artifact. Guarded by sessionsLock. A null value means explicitly cleared.
     private readonly Dictionary<IPAddress, PeerDspChain?> peerDspByAddress = new();
+    // Split-recording tap: one callback shared by every session (each passes its own Endpoint), plus
+    // whether to tap raw or shaped. Set on all current sessions and inherited by new ones, like the DSP.
+    private Action<IPEndPoint, ReadOnlyMemory<float>>? recordTap;
+    private bool recordTapRaw;
     private SessionPlayout[] sessionsSnapshot = [];
     // Per-route scratch. Each IWaveProvider surface (Mixed / WasapiLane / AsioLane) runs on
     // its own consumer thread in BothIndependent mode (WASAPI master producer + ASIO render
@@ -153,6 +157,22 @@ internal sealed class PlayoutEngine : IWaveProvider
         }
     }
 
+    /// <summary>Sets (or clears with null) the split-recording tap on every current and future session.
+    /// <paramref name="raw"/> selects the pre-pan/EQ (bypass) or post (shaped) block.</summary>
+    public void SetRecordTap(Action<IPEndPoint, ReadOnlyMemory<float>>? tap, bool raw)
+    {
+        lock (sessionsLock)
+        {
+            recordTap = tap;
+            recordTapRaw = raw;
+            foreach (var s in sessions.Values) s.SetRecordTap(tap, raw);
+        }
+    }
+
+    /// <summary>Fired once per rendered block, right after the mixed received tap — the block boundary a
+    /// single-file "bypass" recording uses to flush its per-peer sum.</summary>
+    public Action? OnRecordBlockComplete { get; set; }
+
     public WaveFormat WaveFormat { get; } = WaveFormat.CreateIeeeFloatWaveFormat(MixSampleRate, MixChannels);
 
     /// <summary>Legacy property returning the Mixed route's target. Used by code paths that
@@ -326,6 +346,7 @@ internal sealed class PlayoutEngine : IWaveProvider
                 // Inherit this peer's pan+EQ too, so a mid-stream / reconnect session is shaped from
                 // frame zero rather than only on the next SetPeerDsp call.
                 if (peerDspByAddress.TryGetValue(endpoint.Address, out var chain)) sp.SetDsp(chain);
+                if (recordTap is not null) sp.SetRecordTap(recordTap, recordTapRaw);
                 sessions[key] = sp;
                 sessionsSnapshot = sessions.Values.ToArray();
             }
@@ -801,6 +822,7 @@ internal sealed class PlayoutEngine : IWaveProvider
         // BothIndependent; without the tag both ended up in one recorder ring, doubling the
         // file's effective sample rate).
         DispatchReceivedSamples(mixBuf.AsMemory(0, outFloats), route);
+        OnRecordBlockComplete?.Invoke();
 
         Buffer.BlockCopy(mixBuf, 0, buffer, offset, outFloats * sizeof(float));
         return count;
@@ -877,6 +899,7 @@ internal sealed class PlayoutEngine : IWaveProvider
         // wasapi-slot ring (canonical single-lane slot in classic modes), so this fires
         // exactly once per real-time second.
         DispatchReceivedSamples(mixBuf.AsMemory(0, outFloats), RenderRoute.Mixed);
+        OnRecordBlockComplete?.Invoke();
 
         Buffer.BlockCopy(mixBuf, 0, buffer, offset, outFloats * sizeof(float));
         return count;

src/RemSound.Receiver/SessionPlayout.cs

@@ -101,6 +101,13 @@ internal sealed class SessionPlayout : IDisposable
     // Per-peer pan + EQ, or null when this peer isn't shaped. Built on the UI thread and swapped in
     // atomically (volatile reference); the audio thread reads it once per block. See PeerDspChain.
     private volatile PeerDspChain? dsp;
+    // Split-recording tap: when set, each block this session produces is handed to the recorder as this
+    // one peer's audio — RAW (before pan/EQ) when recordRaw, else SHAPED (after). Set/cleared on the UI
+    // thread; read once per block on the audio thread. recordScratch is a reusable copy so the tap never
+    // allocates and never hands out the live output span.
+    private volatile Action<IPEndPoint, ReadOnlyMemory<float>>? recordTap;
+    private volatile bool recordRaw;
+    private float[] recordScratch = new float[2048];
     // Per-session RNG for noise concealment. Seeded from process-level Shared so each session
     // gets a different sequence — but we don't care about reproducibility, just character.
     private readonly Random concealRng = new(Random.Shared.Next());
@@ -338,6 +345,22 @@ internal sealed class SessionPlayout : IDisposable
     /// next block. Called from the UI thread; the audio thread reads the reference lock-free.</summary>
     public void SetDsp(PeerDspChain? value) => dsp = value;
 
+    /// <summary>Sets (or clears with null) this session's split-recording tap. <paramref name="raw"/> =
+    /// deliver the block before pan/EQ (bypass); otherwise after. Takes effect on the next block.</summary>
+    public void SetRecordTap(Action<IPEndPoint, ReadOnlyMemory<float>>? tap, bool raw)
+    {
+        recordRaw = raw;
+        recordTap = tap;
+    }
+
+    private void EmitRecordTap(Action<IPEndPoint, ReadOnlyMemory<float>> tap, Span<float> block, int frames)
+    {
+        int n = frames * 2;
+        if (recordScratch.Length < n) recordScratch = new float[n];
+        block[..n].CopyTo(recordScratch);
+        tap(Endpoint, recordScratch.AsMemory(0, n));
+    }
+
     /// <summary>UTC time of the most recent successful audio write. Used by <see cref="AudioReceiver"/>
     /// to prune long-idle sessions so the dictionary doesn't grow unboundedly.</summary>
     public DateTime LastWriteUtc { get; private set; } = DateTime.UtcNow;
@@ -628,11 +651,16 @@ internal sealed class SessionPlayout : IDisposable
 
         // Read through the resampler and apply concealment on full underruns.
         ReadThroughResampler(output, outFrames);
+        // Split-recording tap, RAW variant — grab this peer's block BEFORE pan/EQ (bypass recording).
+        var tap = recordTap;
+        if (tap is not null && recordRaw) EmitRecordTap(tap, output, outFrames);
         // Per-peer pan + EQ: this peer's block is fully decoded and isolated here, immediately before
         // PlayoutEngine sums it into the mix — so shaping is per-peer and pre-mix, and being per-sample
         // it adds no buffering latency. Null (unshaped peer) skips the whole stage.
         var d = dsp;
         d?.Process(output, outFrames);
+        // Split-recording tap, SHAPED variant — after pan/EQ (the default, "record what you hear").
+        if (tap is not null && !recordRaw) EmitRecordTap(tap, output, outFrames);
         return outFrames;
     }