[Bug]: macOS native capture silently discards the webcam track on long recordings #253

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Describe the bug

On the macOS native capture path the webcam is buffered entirely in memory and only written at finalize. Past ~2 GB the finalize step throws, the error is swallowed, and the session is saved screen-only. No toast, no failure state — the editor opens normally with the camera track simply absent.

A 23-minute take (webcam at BITRATE_BASE 18 Mbps ≈ 2.9 GB) lost the webcam. Shorter takes in the same app session saved fine.

Cause, current on main:

1. The native path builds the webcam handle with no fileName, selecting buffering — nothing reaches disk during capture:

// src/hooks/useScreenRecorder.ts:1323
nativeWebcamRecorder = createRecorderHandle(webcamStream.current, {
  mimeType: selectMimeType(),
  videoBitsPerSecond: BITRATE_BASE,
});

// src/hooks/recorderHandle.ts:43
let mode: "pending" | "streaming" | "buffering" = fileName ? "pending" : "buffering";

The legacy path at useScreenRecorder.ts:1771 passes the filename and streams to disk, so it is unaffected.

2. Finalize flattens the whole recording into one ArrayBuffer for IPC:

// src/hooks/useScreenRecorder.ts:605-613
const fixedWebcamBlob = await fixWebmDuration(webcamBlob, duration + webcamHeadStartMs);
return { videoData: await fixedWebcamBlob.arrayBuffer(), ... };
} catch (error) {
  console.error("Failed to finalize native macOS webcam recording:", error);
  return undefined;
}

3. undefined makes the guard at :639 skip attachNativeMacWebcamRecording, so the session is written with no webcamVideoPath. Only console.error fires; the user is never told.

Expected behavior

Stream the webcam to disk on the native path as the legacy path already does. Failing that, surface a toast when the webcam fails to attach — silently discarding a completed take is the worst available outcome.

To Reproduce

1. macOS, webcam enabled, start a recording (native capture).
2. Record 20+ minutes.
3. Stop.
4. Editor opens with screen + audio, no camera, no error.

Screenshots

No response

OS

macOS

OS Version

macOS 26.5.2

Browser

None

Device Type

Laptop

Additional context

Session file written for the failed take:

{ "screenVideoPath": ".../recording-<id>.mp4", "createdAt": <id>, "cursorCaptureMode": "editable-overlay" }

versus a short take from the same app session:

{ "screenVideoPath": ".../recording-<id>.mp4", "webcamVideoPath": ".../recording-<id>-webcam.webm", ... }

The camera streamed for the full take — macOS cameracaptured, recording ran 09:29:54–09:52:56:

09:28:53.592  -[CMIOExtensionProvider startStreamForClientID:streamID:reply:]
09:52:56.942  -[CMIOExtensionProvider stopStreamForClientID:streamID:reply:]

The main process crossed the 2 GB file-backed write threshold mid-recording, consistent with Chromium paging the buffered blob to blob_storage:

Event:   disk writes
Writes:  2149.48 MB of file backed memory dirtied over 1564 seconds,
         exceeding limit of 24.86 KB per second over 86400 seconds

Same machine, same webcam, one app session:

Observed on 1.7.0; the code paths above are current on main. Plausibly the same root cause as #41 — "something failed but it was silent".