Doug Johnson Productions

Scope guide · Sound & timing

Audio / Video Sync

Measure repeated flash-and-beep events and use offset and spread to investigate timing.

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Learn & Reference / Scope library / Audio / Video Sync

Is audio arriving later than picture?

Add this view from Add scope > Audio / Video Sync, then choose the input you want to inspect. Use the pane's i button for its in-app reading guide.

Read this example.

Application-rendered timing fixture showing a +20.0 ms source-timestamp offset.
Application-rendered timing fixture showing a +20.0 ms source-timestamp offset. Click the image for a larger view.
  1. Audio − video: +20.0 ms means audio is later than video.
  2. Median, spread and pair count describe event evidence. This fixture has one detected pair.
  3. The final line identifies source timestamps as the basis. Other paths can use arrival-time estimates.

Try it yourself.

  1. Feed a suitable flash-and-beep test through the intended path.
  2. Use brief full-frame white flashes and simultaneous beeps at least two seconds apart, with 100 ms of preceding silence.
  3. Collect several pairs and compare median and spread with the stated timing basis.

Useful controls.

  • Calibration accounts for a known offset.
  • Pair count and last-event age describe recent evidence.
  • A ±500 ms window pairs candidate events.

Use a test signal and review the timing basis. Resume after a frozen video selection to collect fresh timing events.