How away-detection works (and how to tune it).

Auto-loop is what makes MeetingDouble feel like magic: you stand up, the loop kicks in, you sit back down, your live feed comes back. The only way that works is if the “he left the desk” signal is correct almost every time. False positives interrupt your real face mid-sentence. False negatives miss the moment you actually walked away.

MeetingDouble uses four signals. The default policy is: switch to loop only when all four agree the user is gone.

The four signals

1. Vision face-presence

The webcam frame is sampled at 1 in every 10 frames (so ~3 Hz at a 30 fps capture) and fed to Apple’s VNDetectFaceRectanglesRequest. If the last detection is older than the threshold (default 5 seconds), this signal flips to away. Running every frame would melt battery; every 10th is the cheapest rate that catches a real walk-off within 0.3 s.

2. Voice activity

AVAudioEngine taps the default input device. A simple energy + zero-crossing VAD reports whether you’ve spoken in the last second. Mic audio is never recorded or sent anywhere — only the “speaking yes/no” boolean is used. If you’re actively talking, the loop will not engage even if Vision lost your face for a moment.

3. HID idle

IOHIDIdleTime reports how long since the last mouse move, key press, or trackpad touch. The default threshold is 20 s. This is the slowest signal — it has to be, otherwise glancing away to read a doc would trigger the loop.

4. Manual hotkey

Cmd+Shift+A toggles loop mode on or off immediately and overrides all other signals. Useful when you know you’re about to step out for coffee and don’t want to wait for the four-sensor consensus. Press again to return to live.

Why all four must agree

Each signal alone produces false positives. Vision misses your face if you turn 90 degrees. The mic stays silent during normal listening. HID idle triggers any time you read for 20 seconds. Combining them is the only way to get a clean decision:

• Reading a doc, mouth closed, no mouse for 20 s → Vision sees you, no switch. Correct.
• You stood up but the music is on → mic detects audio energy but voice activity isn’t voice, ignored. Vision and HID agree you’re gone. Loop engages. Correct.
• You glanced at your phone → Vision still sees you, no switch. Correct.
• You walked away → Vision missing for 5 s, voice silent, HID idle for 20 s. Loop engages. Correct.

Where to tune it

Open Settings → General. The relevant controls:

• Auto Loop toggle (also available in the menubar popover) — kills auto-detection entirely and gives you only the manual hotkey.
• Face missing threshold — radio between 2s, 5s, 10s, 30s, 60s. Default is 5 s. Lower it if you want the loop to kick in fast (good for short bathroom breaks). Raise it if you’re a person who turns their head a lot when you think.
• HID idle threshold — slider from 5 s to 120 s. Default 20 s. Lower values feel snappy but trigger when you’re reading; higher values feel sluggish.
• Require voice silence — checkbox, default on. Turn off if you use a separate USB mic that MeetingDouble can’t see, otherwise the loop will never engage.
• Override hotkey — defaults to Cmd+Shift+A. Rebind from this field. Any modifier combination is allowed.

Coming back to live

Returning is the opposite of the away decision but stricter. As soon as Vision sees your face on a single sampled frame, MeetingDouble waits for the loop to hit a head-neutral frame (front-facing, eyes open) and then crossfades 4 frames back to the live feed. The mic stays muted until you click I’m backin the menubar — so you can’t get caught chewing.

What the menubar tells you

The MeetingDouble menubar icon has three states:

• Solid green — live feed is going to Zoom/Meet/Teams.
• Pulsing amber — loop is playing, you’re “away” by consensus.
• Red — virtual camera failed to start. Open the popover for the reason.

Battery cost

Realistic measurements on M2 MacBook Air: Vision sampling at 1-in-10 is ~0.4% CPU. VAD is ~0.2%. HID idle is free. The biggest cost is the camera capture itself, which Zoom is already paying for anyway. MeetingDouble adds maybe 30 minutes off your day’s battery life on a typical meeting-heavy schedule.