> For the complete documentation index, see [llms.txt](https://docs.timeinpixels.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.timeinpixels.com/nobe-omniscope/features/av-sync-measurement.md).

# A/V Sync Measurement

> **Beta, OmniScope 1.11.54 and later.** This feature requires a Pro license and an input that provides corresponding native audio and video timestamps.

A/V Sync Measurement compares a visible flash with an audio beep from the same source. It reports their offset in milliseconds and frames:

* **Audio early** means the beep timestamp occurs before the flash.
* **Audio late** means the beep timestamp occurs after the flash.
* **Aligned at measurement resolution** means no offset was detected at the source's video-frame resolution.

Measurement continues while the A/V Sync window is closed. Use the **Toggle A/V Sync window** action for the input to open or close it; the action can be assigned in the [Action Editor](/nobe-omniscope/action-editor.md).

## Setup

1. Connect a source that carries both video and native audio, then select **Native audio** for that input.
2. Enable **A/V Sync (beta)** for the input.
3. Choose **Generic flash/beep** or **Sync-It flash mode (beta)**.
4. Click the flash in the decoded-input preview to place the measurement region. Use a tight region for a small LED, or **Full frame** for a large flash.
5. Select the audio channel and adjust the flash and beep thresholds if required.
6. Set **Max offset** to less than half the interval between repeated flashes.

The result panel reports the offset, early/late direction, video sampling interval, region brightness, audio peak, and the age of the latest measurement. It also distinguishes missing audio or video, unavailable timestamps or channels, ambiguous events, and stale results.

## Accuracy and limitations

The measurement uses audio and video source timestamps rather than UI timing or QC Timeline timecode. Video accuracy is limited by the source frame interval, camera exposure, and capture-device timestamp behavior.

Identical periodic flashes cannot distinguish a true offset from an offset of one or more complete flash cycles. For unknown long delays, use an irregular flash/beep sequence. The Sync-It preset uses the generic onset detector and is not certified Sync-It protocol support.