title: Tap-to-focus, interruptions, stabilization description: Three small but common controls: focus / exposure point of interest, session interruption notifications, and movie stabilization mode.

The three main things you need to worry about when using AVCaptureSession are:

• tap-to-focus and tap-to-meter (focus / exposure point of interest on the device)
• session interruption notifications (a phone call, another app grabbing the camera, system pressure)
• video stabilization on the movie output

These are all device / connection level — they don't change how you wire up inputs and outputs.

#Tap-to-focus / tap-to-meter

AVCaptureDevice exposes a focus point and an exposure point. Both are normalized to 0..1 of the sensor frame (not your preview view), with (0, 0) at the top-left of the landscape-oriented sensor. Most apps map a tap on the preview view into normalized sensor coordinates and then write both the focus point and the exposure point at once:

const camera = AVCaptureDevice.default("video")!

// Whenever the user taps the preview view, translate the tap into
// normalized sensor coords (your preview layer can do this for you in native;
// in JS you typically pre-compute once per layout).
function tap(at: { x: number; y: number }) {
  if (camera.isFocusPointOfInterestSupported) {
    camera.setFocusPointOfInterest(at)
    camera.setFocusMode("autoFocus")          // single-shot AF at that point
  }
  if (camera.isExposurePointOfInterestSupported) {
    camera.setExposurePointOfInterest(at)
    camera.setExposureMode("continuousAutoExposure")
  }
}

A few gotchas:

• setFocusPointOfInterest and setExposurePointOfInterest are silent no-ops on devices that don't support them — guard with the is*Supported flag if you want to surface that to the user.
• These setters acquire the device configuration lock internally; you don't need to wrap them in lockForConfiguration().
• Setting only the point doesn't trigger a refocus — you also need a focus mode (autoFocus for one-shot, continuousAutoFocus for tracking) and / or an exposure mode change.

#Session interruptions

iOS will sometimes pull the camera out from under you: an incoming call, another app moving to the foreground with multi-app support, FaceTime taking the front camera, system thermal pressure. The session keeps running in the background but is paused — your preview will look frozen until iOS hands the hardware back.

Subscribe to know when this happens:

session.addInterruptionListener((event, reason) => {
  if (event === "began") {
    // Show a "camera unavailable" overlay.
    console.log("interrupted because:", reason)
  } else {
    // Hide the overlay; the session will resume on its own.
    console.log("interruption ended")
  }
})

reason is one of:

event === "ended" always passes an empty string — there is no "reason" for the resume.

You don't need to call startRunning() again after "ended". The session resumes automatically.

#Video stabilization

The system can apply optical / sensor stabilization on the recorded video. You set a preferred mode on the movie output's video connection — the system decides whether to actually activate it based on the active format and device capability. Always read back the active mode if you want to know what's really happening.

const movieOutput = new AVCaptureMovieFileOutput()
session.addOutput(movieOutput)

// Pick one before you start recording.
movieOutput.setVideoStabilizationMode("auto")

// After startRunning(), this reflects what the system actually picked:
console.log("active stabilization:", movieOutput.videoStabilizationMode)

Notes:

• Stabilization is applied per connection, not per session. If you swap the device-input or rebuild the connection, you need to set the mode again.
• setVideoStabilizationMode("...") returns false if the movie output isn't attached to a session yet (no video connection exists). Set the mode after session.addOutput(movieOutput).
• Throwing happens only on an unknown mode string — a misspell will surface immediately.
• videoStabilizationMode is active, not requested. The system may downgrade or disable it silently if the active format doesn't support it.