---
title: "Sync External Audio to Video – Mic or Recorder | sync.video"
description: "Line up a lav mic, pocket recorder or phone voice memo with your camera clip by its sound and swap in the clean audio. Picture untouched, nothing uploaded."
url: https://sync.video/sync-external-audio
---

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# Sync audio recorded separately to your video

Drop the camera clip and the recording from your mic or recorder. They’re lined up by their sound, and the camera’s scratch audio is replaced with the clean track.

To sync audio recorded separately, drop the video and the recording together: the two soundtracks are compared, the recording slides into place, and **Replace the camera sound** puts the clean track under your picture. Press **Export video** and you have one file with good sound in sync.

This is the everyday version of dual-system sound: a camera or phone films, while a lavalier, a wireless mic kit, a handheld recorder or another phone in a pocket records the voice. The camera still needs its own microphone switched on, because its rough scratch sound is the reference the recording is matched against. Matching is precise to well under a millisecond when both heard the same words.

If there is no second recording and the one file is simply out of step, use [fix the audio sync](https://sync.video/fix-audio-sync) instead. For three or more devices, the [multicam hub](https://sync.video/sync-multiple-cameras) covers batch syncing and timeline export.

Matching by waveform: the same clap reaches the camera and the separate recorder, so the two waveforms have the same shape. Sliding one until the shapes overlap gives the offset.

## How to sync external audio to video

1. ### Drop the clip and the recording
Select the video and the audio file together and drop them on **Drop your video and its sound files**, or press **Choose files**. WAV, MP3 and M4A recordings all open; on a phone, pick both from Files.
2. ### Check the match
Look for **Sure match** next to the recording, then play a few words with Space. If it sounds doubled or echoey, press **Try the next match**, or nudge the recording with \[ and \] (10 ms; Shift for 1 ms).
3. ### Choose the sound
**Replace the camera sound** is already selected, with the recording under **Use the sound from**. Prefer some room tone? Choose **Mix them** and turn the camera down with its level slider.
4. ### Export video
Press **Export video** (Ctrl/Cmd+Enter) and download the result. The picture is copied as it is; a recording in a format the file can hold is copied too.

## Recording so the sync works first time

* Keep the camera’s own microphone on. Even a muffled built-in mic gives a usable reference; a camera with no sound at all can only be lined up by eye.
* Start the recorder before the camera and stop it after. A recording that covers the whole clip is easiest to place.
* Clap once, in shot, near the start. It isn’t required, but a sharp spike makes the match certain. The [digital clapperboard](https://sync.video/digital-clapperboard) does this with a phone.
* Use 48 kHz on the recorder if it offers a choice. 44.1 kHz works too; it is converted when the sound is rebuilt.
* For long takes, check the drift line in the file list after matching. Cheap recorders and phones can run a little fast or slow over half an hour.

### Phone voice memos as a recorder

A second phone in a pocket with a clip-on mic is a surprisingly good recorder. Voice memo apps often save compressed M4A files, which open fine here. Turn off any setting that skips silences or enhances speech, since both change the timing of the recording and make it impossible to line up for the whole length.

## Replace, mix or keep both

__What each sound choice writes into the new video__
| Choice                       | You hear                                                 | Good for                                          |
| ---------------------------- | -------------------------------------------------------- | ------------------------------------------------- |
| **Replace the camera sound** | Only the recording you pick under **Use the sound from** | Interviews, vlogs and talking heads               |
| **Mix them**                 | Every file, each at its own level                        | Adding a little room tone or audience under a lav |
| **Keep both**                | Each sound as its own track                              | Editing the mix later in another app              |
| **Keep the camera sound**    | The camera only                                          | When you only want synced copies or a timeline    |

When one recording simply replaces the camera’s, and the recording is in a format the video file can hold (AAC in an MP4, for example), its sound is copied without re-encoding. A mix, a fade or a drift correction means the sound is decoded and encoded once, at 192 kbps AAC for MP4 and MOV files.

## When the sound drifts apart

A camera and a recorder keep time with separate clocks. Over a short clip that never matters; over forty minutes a difference of a few parts per million can open a gap of a frame or more. When the files overlap by at least 30 seconds, sync.video measures the offset at several points and, if the gap grows steadily, shows the drift next to the recording and stretches that sound in the export to stay in step from start to finish.

If a single video has sound that slips out on its own, with no second recording involved, the cause and the fix are different: see [fix audio drift](https://sync.video/fix-audio-drift).

## Questions about syncing a separate recording

### How do I sync audio from my phone with a video from my camera?

Drop the camera clip and the phone’s audio file together. As long as the camera’s microphone also picked up the voice, the two are matched by their sound automatically. Then keep **Replace the camera sound** and export.

### Do I need a clapperboard?

No. Speech alone is usually enough. A clap at the start makes the match quicker to confirm and helps when the room is noisy.

### My camera recorded no sound at all. Can it still be synced?

Not automatically, because there is nothing to compare. You can drag the recording into place on the timeline by eye, using a moment you can see and hear, such as a clap.

### Can I keep a bit of the camera sound under the recording?

Yes. Choose **Mix them**, then lower the camera’s level slider until it adds a little room tone without muddying the voice.

### Will my video be re-encoded?

The picture never is: its compressed frames are copied. The sound is copied too when it can be, otherwise encoded once at a high bitrate.

### Which recorders work?

Any device that saves a common sound file: WAV, MP3, M4A, AAC, FLAC or Ogg. That covers clip-on wireless kits, handheld recorders and phone voice memo apps. Unusual formats are converted on your device first.

## More in sync multiple cameras

* [ Sync multiple cameras and recorders Two to eight angles and audio recorders lined up by their shared sound, for multicam editing. ](https://sync.video/sync-multiple-cameras)
* [ Add music or audio to a video Put a song, voiceover or recording on a clip: mix or replace the sound, set the start, fade out. ](https://sync.video/add-audio-to-video)
* [ Fix audio and video out of sync Work out whether the file or the playback is at fault, then fix the delay or measure it. ](https://sync.video/fix-audio-sync)
* [ A digital clapperboard on your phone A free slate with scene, take and a timed flash and crack that syncs cameras and recorders. ](https://sync.video/digital-clapperboard)
* [ Sync audio and video online Drop one video to fix its delay, or several files to line them up by their sound. ](https://sync.video/)