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How to sync audio and video on a Mac

Final Cut Pro syncs clips by their sound with one command; iMovie has no automatic sync at all. Here is how to do both, and how to let the browser do the matching for iMovie projects.

Drop your video and its sound files

A camera clip plus a separate mic or recorder, or several cameras. They’re lined up by their sound.

MP4 · MOV · MKV · WAV · MP3 · M4A

Matched on your device. Nothing is uploaded.

In Final Cut Pro, select the camera clip and the recording in the browser and choose Clip › Synchronize Clips (Option-Command-G) with Use audio for synchronization ticked. Final Cut makes a new synchronised clip with the two in line and leaves the originals untouched.

iMovie has no command that lines clips up by their sound, so there you either nudge the recording by eye against its waveform, or sync the files first and bring a finished clip into iMovie. The tool on this page does that matching in Safari or Chrome and can export one video with the recorder’s sound in place, ready for an iMovie project.

For the same job in other editors see the Premiere guide and the DaVinci Resolve guide. The multicam hub explains how sound matching works and what makes it fail.

Several cameras and a recorder start at different times. Once each is placed at its offset, the shared moment (a clap) sits on one vertical line across every track.

Sync audio in Final Cut Pro with Synchronize Clips

  1. Import both clips

    Import the camera clip and the recorder file into the same event, so both show in the browser.

  2. Select them and choose Synchronize Clips

    Select the two clips, then choose Clip › Synchronize Clips or press Option-Command-G. You can also Control-click and choose it from the menu.

  3. Use the audio

    In the window that opens, make sure Use audio for synchronization is selected, then click OK. Final Cut checks markers, timecode and dates, then refines the alignment with the waveforms.

  4. Edit with the synchronised clip

    A new synchronised clip appears in the browser. Use it in your project, and turn off the camera’s scratch audio in the clip’s audio settings if you only want the recorder.

Several cameras in Final Cut Pro

For two or more angles, make a multicam clip: select every angle and the recorder in the browser and choose File › New › Multicam Clip. In its settings, keep audio-based synchronisation on, and Final Cut lines the angles up by their sound before building the clip you cut between in the angle viewer. As with every waveform method, each angle needs some sound of its own.

If Final Cut can’t sync the clips

  • Apple notes that analysing the audio can take a while on long clips, and some recordings simply don’t suit it. Trimming a long recorder file near the take helps.
  • A silent camera can’t be matched by sound. Add a marker on a visible clap in each clip and sync by markers instead.
  • If a long take drifts out by the end, the recorder and camera clocks differ; Final Cut aligns once and doesn’t stretch the audio.

Lining up a recording in iMovie

iMovie for Mac can show waveforms and can separate a clip’s sound with Modify › Detach Audio (Option-Command-B), but it has no automatic sync. Lining up a recorder by hand works, it just takes patience:

  1. Put the camera clip on the timeline and drag the recording under it, roughly in place.
  2. Make sure waveforms are showing, then zoom the timeline right in around a clap or a sharp word.
  3. Drag the recording until its spike sits directly under the camera sound’s spike, then play it to check for an echo.
  4. Lower the camera clip’s own volume to zero once it sounds right.

Zooming far enough to place sound to the frame is fiddly in iMovie, and a near miss of a frame or two makes speech sound hollow. The quicker route is below. If all you want is a song or voiceover under an iMovie clip, with no recording to match, add audio to a video sets its start, level and fade in one go.

Let the browser do the matching

  1. Drop the camera clip and the recording onto the tool at the top of this page. They are matched by their sound in seconds; check for Sure match.
  2. Choose Replace the camera sound and press Export video. The picture is copied as it is, so iMovie gets the same quality you shot.
  3. Import the new file into iMovie and edit as normal: the sound is already in sync.

Final Cut Pro users can go further: with several angles, press FCPXML (Final Cut, Resolve) under More options and open the file in Final Cut, keeping it beside the footage so the clips relink by name. Need a clap that every camera can see and hear? The digital clapperboard runs on any phone.

Questions about syncing audio on a Mac

Can iMovie sync audio automatically?

No. iMovie has no command that lines up two clips by their sound. You can line them up by eye using the waveforms, or sync them first on this page and import one finished file.

What is the shortcut for Synchronize Clips in Final Cut Pro?

Option-Command-G, with the clips selected in the browser. Tick Use audio for synchronization for waveform matching.

Does Synchronize Clips change my original files?

No. Final Cut creates a new synchronised clip and leaves the original clips as they were.

How do I sync several cameras in Final Cut Pro?

Create a multicam clip from the selected angles with audio synchronisation turned on. Final Cut lines them up by sound and builds a clip you can switch angles in.

Does this work in Safari?

Yes, in a recent version of Safari on macOS, as well as Chrome, Edge and Firefox. Nothing is installed and the files stay on your Mac.