How to sync video with separately recorded audio

Separately recorded sound can be synced to video in Video by Zaweba in two ways. Select the camera clip and the sound clip on the timeline and use Synchronise by sound, which lines them up to the millisecond by matching what both recorded. Or use Merge to link a camera clip with its separate sound file so they behave as one. Both work offline on your own PC.

Recording sound separately, on a phone, a lapel microphone or a portable recorder, gives far better sound than most cameras' built-in microphones. The catch has always been lining the two up afterwards, and that's what these tools take care of.

What the camera needs to record

Synchronising by sound needs both recordings to have heard the same thing. Keep the camera's own microphone on, even though you won't use its sound in the end. Its rough recording is the guide that the good recording is matched against.

A clap at the start, in view of the camera and in earshot of both microphones, helps a lot. It's a sharp, distinct sound that leaves no doubt, and it's also something you can line up by eye on the waveform if you ever need to.

Lining them up with Synchronise

Put the camera clip on a video track and the separate sound on a sound track below, roughly in the right place. Select both and use Synchronise, choosing sound as the method. Video by Zaweba compares the two recordings and moves the clips so they match, to the millisecond.

Synchronise can also line clips up by start, end, timecode or the first clip marker, which helps when you have timecode from both devices or when you've marked a clap by hand.

Play the result and watch lips and hands. If speech and mouth movement agree, you're done. Then mute or delete the camera's scratch sound so only the good recording is heard.

Linking them with Merge

Merge goes a step further. It links a camera clip with its separately recorded sound file, so the two move, trim and split together like a clip recorded with sound. That's the tidy way to work when you have many takes: merge each pair once, then edit without worrying that the sound will slip out of sync as you trim.

Linking can also be done by hand. Ctrl+L links selected picture and sound, and Ctrl+Shift+L unlinks them if you need to adjust one separately.

Several cameras and one recorder

For an event filmed on two or three cameras with a single sound recorder, the multi-camera tools do the same job on a bigger scale. Clip > Multi-camera builds a source lined up by sound, and Ctrl+Shift+1 to 9 chooses which camera's sound you use, or you can sync the recorder in alongside.

Getting the best from the good sound

Once synced, the separate recording usually needs only a little help. Noise reduction learns the noise from the clip's quietest half-second, voice EQ presets add clarity, and on export the mix is levelled to -14 LUFS. Auto-ducking keeps any music under the speech.

One thing to watch: on very long recordings, some cheap devices drift slowly over time. If the start is in sync and the end isn't, split the sound and sync each section again. For ordinary takes of a few minutes, a single sync holds all the way.