Gyro data, baked into your footage.

StealthLogger logs your iPhone's gyroscope at 100 Hz while you shoot, then writes it into the video file as a CAMM track. Gyroflow reads it straight out — no sidecar log to keep paired with the clip for the rest of its life.

Rotation rate rad/s · sample trace

gx
gy
gz
100 Hz

writing › 1754654321123456,0.0000,0.0000,0.0000,0.0000,0.0000,-1.0000

Signal path

Record

Start a session, then shoot with the Camera app. Motion is sampled in the background and written straight to disk as you go.

stealthlog_20260808_142208.gcsv
Embed

Pick your clips. Each is matched to the session recorded around the same time, then remuxed — the video is copied, never re-encoded.

stealth_remux_20260808_143112.mov
Stabilise

Open the result in Gyroflow. The CAMM track is picked up on import with nothing to line up by hand.

Gyroflow · auto-detected

The readout

You spend the shoot inside a different app. The awkward question is whether logging is still alive back there.

So the session reports from the Lock Screen for as long as it runs: elapsed time, samples captured, and the rate they're actually arriving at.

That last figure is the one worth watching. It should sit near 100 Hz — if iOS throttles the sensor or deprioritises the app, it sags, and you find out during the shoot instead of after it.

An iPhone Lock Screen showing StealthLogger's Live Activity: Logging gyro, 996 samples, 0:16 elapsed, 99 Hz

Hands-free

Four actions — Start Gyro Log, Start Gyro Log (Stealth), Stop Gyro Log, and Is StealthLogger Active — are available system-wide the moment the app is installed: Siri, the Shortcuts app, Spotlight, the Action Button. No setup step.

Stealth Start and Stop run without opening the app at all — no Lock Screen indicator, no switching away from whatever you're filming with. Is StealthLogger Active returns a plain Boolean, so a shortcut can check before deciding what to do next.

The iOS Shortcuts app searching StealthLogger, listing four actions: Is StealthLogger Active, Start Gyro Log, Start Gyro Log (Stealth), and Stop Gyro Log

Screens

StealthLogger's Record tab during an active session — Session running

The Gyro Logs tab, listing .gcsv files grouped under Today and Past — Logs by day

The Encoded Media tab, listing finished .mov files with their sizes — Finished clips

Spec

Sampling: Gyroscope and accelerometer, 100 Hz
Log format: Gyroflow IMU log v1.3 · orientation YxZ · tscale 1e−6
Embedding: Native CAMM metadata track, remuxed without re-encoding
Clip matching: By creation timestamp, within a 300-second window
Batch: Many clips per session, each matched independently
Readout: Live Activity on the Lock Screen and Dynamic Island
Automation: Siri, Shortcuts, Spotlight, Action Button — start, stop, check status
Requires: A physical iPhone · iOS 16, or 16.2 for the readout