diff --git a/src/TeamsISO.Engine/Pipeline/IRecorderSink.cs b/src/TeamsISO.Engine/Pipeline/IRecorderSink.cs
new file mode 100644
index 0000000..9004f66
--- /dev/null
+++ b/src/TeamsISO.Engine/Pipeline/IRecorderSink.cs
@@ -0,0 +1,58 @@
+namespace TeamsISO.Engine.Pipeline;
+
+/// <summary>
+/// Tap point for per-ISO output recording. Each <see cref="IsoPipeline"/> can be
+/// wired with one recorder; when present, every <see cref="ProcessedFrame"/> that
+/// flows from <see cref="FrameProcessor"/> to <see cref="NdiSender"/> is also fed
+/// to the recorder for persistence to disk.
+///
+/// Lifecycle:
+///   1. <see cref="Open"/> is called once when the pipeline starts (or restarts).
+///   2. <see cref="WriteFrame"/> is called for every processed frame, in order.
+///   3. <see cref="Close"/> is called once when the pipeline stops or fails.
+///
+/// Implementations must be tolerant of out-of-order calls (Close before Open,
+/// double Close, WriteFrame after Close) — the supervisor's restart logic can
+/// race in unusual ways. The simplest correct implementation is to track an
+/// <c>_isOpen</c> flag and short-circuit when not open.
+/// </summary>
+public interface IRecorderSink : IAsyncDisposable
+{
+    /// <summary>
+    /// Open the underlying file/encoder and prepare to receive frames. Width/Height
+    /// match the pipeline's normalized output resolution; FPS is the target framerate
+    /// (incoming frames may arrive with timing jitter, but the recorder writes at the
+    /// nominal rate for downstream playback consistency).
+    /// </summary>
+    /// <param name="participantDisplayName">Used to derive the output filename.</param>
+    /// <param name="outputDirectory">Directory under which the recording is created.</param>
+    /// <param name="width">Frame width in pixels.</param>
+    /// <param name="height">Frame height in pixels.</param>
+    /// <param name="fps">Nominal framerate.</param>
+    void Open(string participantDisplayName, string outputDirectory, int width, int height, double fps);
+
+    /// <summary>
+    /// Write one processed frame. Implementations should not block — if encoding is
+    /// expensive, queue the frame to a worker thread and return promptly. Returning
+    /// false means the recorder dropped the frame (disk full, queue overflow); the
+    /// pipeline carries on regardless so a recorder failure never kills the live ISO.
+    /// </summary>
+    bool WriteFrame(ProcessedFrame frame);
+
+    /// <summary>
+    /// Flush and finalize the output. Idempotent.
+    /// </summary>
+    void Close();
+
+    /// <summary>True between successful <see cref="Open"/> and <see cref="Close"/>.</summary>
+    bool IsRecording { get; }
+
+    /// <summary>
+    /// Drop a timestamped marker into the recording. Used by the operator to
+    /// chapter a recording in real time — "host intro starts here", "guest
+    /// answer", etc. — so post-production can jump to the right moment without
+    /// scrubbing through the raw stream. The label is free-form; an empty
+    /// label means "unnamed marker." No-op when not recording.
+    /// </summary>
+    void AddMarker(string label);
+}
diff --git a/src/TeamsISO.Engine/Pipeline/RawBgraRecorderSink.cs b/src/TeamsISO.Engine/Pipeline/RawBgraRecorderSink.cs
new file mode 100644
index 0000000..8140858
--- /dev/null
+++ b/src/TeamsISO.Engine/Pipeline/RawBgraRecorderSink.cs
@@ -0,0 +1,256 @@
+using System.IO;
+using System.Text.Json;
+using System.Threading.Channels;
+using Microsoft.Extensions.Logging;
+
+namespace TeamsISO.Engine.Pipeline;
+
+/// <summary>
+/// Concrete <see cref="IRecorderSink"/> that writes the processed BGRA stream to
+/// disk along with a sidecar JSON manifest and an <c>ffmpeg.cmd</c> conversion
+/// script. We deliberately do NOT depend on Media Foundation, libx264, or any
+/// other native encoder for v1: the engine stays self-contained, and operators
+/// who want H.264 .mkv output can run the generated <c>ffmpeg.cmd</c> after the
+/// recording finishes (FFmpeg on PATH is a common operator install).
+///
+/// Files produced under <c>&lt;outputDir&gt;/&lt;sanitized-display-name&gt;/</c>:
+///   <list type="bullet">
+///     <item><c>video.bgra</c> — raw concatenated frames at <c>width*height*4</c> bytes each.</item>
+///     <item><c>manifest.json</c> — width, height, fps, format, started/ended timestamps,
+///           frame count. Lets a post-processor reconstruct timing without parsing the .bgra.</item>
+///     <item><c>convert.cmd</c> — one-liner that pipes the .bgra into ffmpeg to produce
+///           a final <c>output.mkv</c> at H.264. Operators just double-click.</item>
+///   </list>
+///
+/// Disk pressure: BGRA at 1080p60 is ~500 MB/s, at 720p30 it's ~88 MB/s. A 30-min
+/// recording at the default 720p30 takes ~150 GB. Operators should record at the
+/// lowest acceptable resolution / framerate, or enable recording only on the
+/// participants they intend to keep. A future <c>MediaFoundationRecorderSink</c>
+/// would compress in-process and reduce this 10× — see _NEXT.md.
+///
+/// Threading: writes are serialized through a single bounded channel so the
+/// pipeline's processor thread never blocks on disk I/O. If the disk can't keep
+/// up, frames are dropped (and the manifest's drop counter increments) so the
+/// live ISO output is never delayed.
+/// </summary>
+public sealed class RawBgraRecorderSink : IRecorderSink
+{
+    private readonly ILogger<RawBgraRecorderSink>? _logger;
+    private readonly Channel<ProcessedFrame> _queue;
+    private CancellationTokenSource? _writerCts;
+    private Task? _writerTask;
+    private FileStream? _videoStream;
+    private string? _recordingDir;
+    private int _width;
+    private int _height;
+    private double _fps;
+    private long _framesWritten;
+    private long _framesDropped;
+    private DateTimeOffset _startedAt;
+    private string _displayName = string.Empty;
+
+    // Operator-dropped markers, recorded in wall-clock order. We accumulate them
+    // in memory during the recording and write to manifest.json on Close. Lock
+    // is required because AddMarker can be called from the UI thread while the
+    // writer task drains video frames in the background.
+    private readonly List<MarkerEntry> _markers = new();
+    private readonly object _markersGate = new();
+    private sealed record MarkerEntry(double OffsetMs, string Label);
+
+    public bool IsRecording { get; private set; }
+
+    public RawBgraRecorderSink(ILogger<RawBgraRecorderSink>? logger = null)
+    {
+        _logger = logger;
+        // Bounded queue with DropOldest: if the disk falls behind, lose the
+        // oldest frames and keep recording — better than blocking the pipeline.
+        // 240 frames ≈ 4 seconds @ 60 fps; gives us a buffer for transient
+        // disk hiccups without unbounded RAM growth on a stuck volume.
+        _queue = Channel.CreateBounded<ProcessedFrame>(new BoundedChannelOptions(240)
+        {
+            FullMode = BoundedChannelFullMode.DropOldest,
+            SingleReader = true,
+            SingleWriter = false, // pipeline thread + close() can both write
+        });
+    }
+
+    public void Open(string participantDisplayName, string outputDirectory, int width, int height, double fps)
+    {
+        if (IsRecording) return;
+
+        _width = width;
+        _height = height;
+        _fps = fps;
+        _startedAt = DateTimeOffset.Now;
+        _framesWritten = 0;
+        _framesDropped = 0;
+        _displayName = participantDisplayName;
+
+        var safeName = SanitizeForFileName(participantDisplayName);
+        _recordingDir = Path.Combine(outputDirectory, safeName);
+        Directory.CreateDirectory(_recordingDir);
+
+        var videoPath = Path.Combine(_recordingDir, "video.bgra");
+        // Pre-allocate via FileStream with sequential-scan hint; the writer thread
+        // appends. Buffer size tuned to one full frame so writes are aligned and
+        // we don't fragment on common allocators.
+        var bufferSize = Math.Max(width * height * 4, 64 * 1024);
+        _videoStream = new FileStream(
+            videoPath,
+            FileMode.Create, FileAccess.Write, FileShare.Read,
+            bufferSize: bufferSize,
+            FileOptions.SequentialScan);
+
+        _writerCts = new CancellationTokenSource();
+        _writerTask = Task.Run(() => WriterLoopAsync(_writerCts.Token));
+
+        IsRecording = true;
+        _logger?.LogInformation(
+            "Recorder open: {Path} ({W}x{H}@{Fps:F2}fps)",
+            _recordingDir, width, height, fps);
+    }
+
+    public bool WriteFrame(ProcessedFrame frame)
+    {
+        if (!IsRecording) return false;
+        if (_queue.Writer.TryWrite(frame)) return true;
+        Interlocked.Increment(ref _framesDropped);
+        return false;
+    }
+
+    public void AddMarker(string label)
+    {
+        if (!IsRecording) return;
+        var offsetMs = (DateTimeOffset.Now - _startedAt).TotalMilliseconds;
+        lock (_markersGate)
+        {
+            _markers.Add(new MarkerEntry(offsetMs, label ?? string.Empty));
+        }
+    }
+
+    public void Close()
+    {
+        if (!IsRecording) return;
+        IsRecording = false;
+
+        // Mark the writer queue complete; the writer task drains remaining frames.
+        _queue.Writer.TryComplete();
+        try { _writerTask?.Wait(TimeSpan.FromSeconds(5)); }
+        catch { /* defensive: writer task may have already faulted */ }
+        _writerCts?.Cancel();
+        _writerCts?.Dispose();
+        _writerCts = null;
+        _writerTask = null;
+
+        try { _videoStream?.Flush(); _videoStream?.Dispose(); }
+        catch { /* defensive */ }
+        _videoStream = null;
+
+        if (_recordingDir is not null)
+        {
+            TryWriteManifest();
+            TryWriteFfmpegScript();
+        }
+
+        _logger?.LogInformation(
+            "Recorder closed: {Frames} written, {Dropped} dropped to {Path}",
+            _framesWritten, _framesDropped, _recordingDir);
+    }
+
+    public async ValueTask DisposeAsync()
+    {
+        Close();
+        await Task.CompletedTask;
+    }
+
+    private async Task WriterLoopAsync(CancellationToken ct)
+    {
+        try
+        {
+            await foreach (var frame in _queue.Reader.ReadAllAsync(ct))
+            {
+                if (_videoStream is null) break;
+                try
+                {
+                    // ProcessedFrame.Pixels is a ReadOnlyMemory<byte>; FileStream.Write
+                    // accepts ReadOnlySpan<byte> so we can write without an extra copy.
+                    _videoStream.Write(frame.Pixels.Span);
+                    Interlocked.Increment(ref _framesWritten);
+                }
+                catch (Exception ex)
+                {
+                    _logger?.LogWarning(ex, "Recorder write failed; will count as dropped.");
+                    Interlocked.Increment(ref _framesDropped);
+                }
+            }
+        }
+        catch (OperationCanceledException) { /* expected */ }
+    }
+
+    private void TryWriteManifest()
+    {
+        try
+        {
+            MarkerEntry[] markersSnapshot;
+            lock (_markersGate) { markersSnapshot = _markers.ToArray(); }
+
+            var manifest = new
+            {
+                schema = "teamsiso-recorder/v1",
+                participantDisplayName = _displayName,
+                width = _width,
+                height = _height,
+                fps = _fps,
+                pixelFormat = "BGRA",
+                bytesPerFrame = _width * _height * 4,
+                startedAt = _startedAt.ToString("o"),
+                endedAt = DateTimeOffset.Now.ToString("o"),
+                framesWritten = Interlocked.Read(ref _framesWritten),
+                framesDropped = Interlocked.Read(ref _framesDropped),
+                markers = markersSnapshot.Select(m => new { offsetMs = m.OffsetMs, label = m.Label }).ToArray(),
+            };
+            var json = JsonSerializer.Serialize(manifest, new JsonSerializerOptions { WriteIndented = true });
+            File.WriteAllText(Path.Combine(_recordingDir!, "manifest.json"), json);
+        }
+        catch (Exception ex)
+        {
+            _logger?.LogWarning(ex, "Failed to write recorder manifest.");
+        }
+    }
+
+    private void TryWriteFfmpegScript()
+    {
+        try
+        {
+            // Operators rarely have FFmpeg's exact rawvideo-to-MKV recipe memorized;
+            // ship a one-liner so they can convert by double-clicking. Quotes around
+            // the input filename so paths with spaces still work; -y auto-overwrites
+            // an existing output.mkv if the operator runs the script twice.
+            var script =
+                "@echo off\r\n" +
+                "REM Convert raw BGRA recording to H.264 MKV. Requires FFmpeg on PATH (download from ffmpeg.org).\r\n" +
+                $"ffmpeg -y -f rawvideo -pix_fmt bgra -s {_width}x{_height} -r {_fps:F2} -i video.bgra " +
+                "-c:v libx264 -preset medium -crf 18 -pix_fmt yuv420p output.mkv\r\n" +
+                "if errorlevel 1 (echo FFmpeg failed. Is it installed and on PATH?) else (echo Wrote output.mkv)\r\n" +
+                "pause\r\n";
+            File.WriteAllText(Path.Combine(_recordingDir!, "convert.cmd"), script);
+        }
+        catch (Exception ex)
+        {
+            _logger?.LogWarning(ex, "Failed to write recorder convert.cmd.");
+        }
+    }
+
+    /// <summary>
+    /// Strip characters that would make the display name an invalid Windows
+    /// filename (or path-traversal vector). Empty or all-stripped names fall
+    /// back to "participant" so we always have a usable directory name.
+    /// </summary>
+    private static string SanitizeForFileName(string name)
+    {
+        if (string.IsNullOrWhiteSpace(name)) return "participant";
+        var invalid = Path.GetInvalidFileNameChars();
+        var clean = new string(name.Where(c => !invalid.Contains(c) && c != '.').ToArray()).Trim();
+        return string.IsNullOrEmpty(clean) ? "participant" : clean;
+    }
+}