---
title: "Add Audio to Video – Music, Voice or Mic | sync.video"
description: "Add music, a voiceover or a separate recording to a video: replace its sound or mix them, set where it starts and fade it out. Free, no upload, no watermark."
url: https://sync.video/add-audio-to-video
---

1. [Home](https://sync.video/)
2. [Sync multiple cameras](https://sync.video/sync-multiple-cameras)
3. Add audio to video

Free · runs in your browser

# Add audio or music to a video

Drop a clip and a sound file, slide the audio to where it should start, then mix it with the original or replace it outright. The picture is copied without re-encoding.

To add audio to a video, drop the video and the sound file here together, drag the audio on the timeline to where it should begin, and press **Export video**. By default the new sound is mixed with the clip’s own, each with a level slider, and faded out over the last two seconds; choose **Replace the camera sound** to drop the original sound completely.

The new video is exactly as long as the clip. A song that runs longer is cut at the end of the picture (the fade makes that sound deliberate), and one that is shorter simply ends, leaving silence or the original sound after it. The picture is copied as it was, so there is no loss of quality, no watermark and no upload: it all happens in your browser.

If the audio was recorded at the same time as the video (a clip-on mic, a recorder, another phone), let it line itself up instead: turn on **Match files by their sound** under **More options**, or see [sync external audio](https://sync.video/sync-external-audio). Adding a song and want the cuts to land on its beats? Use [beat sync](https://sync.video/beat-sync) to cut the clips to the music’s beat.

A fixed offset: every sound arrives the same amount late. Moving the whole sound track earlier by that amount lines every clap up with its frame again.

## How to add audio to a video

1. ### Drop the video and the audio
Drag both files onto **Drop a video and the audio to add**, or press **Choose files** and select them together. MP3, M4A, WAV, AAC, FLAC and Ogg sound files all work.
2. ### Set where the audio starts
Drag the audio’s bar on the timeline, or select it and press \[ or \] to move it 10 ms at a time (Shift+\[ and Shift+\] for 1 ms). Press Space to hear the result.
3. ### Balance or replace
With **Mix them**, use each file’s level slider, or its mute button, to set the balance. Choose **Replace the camera sound** to use only the new audio. Set **Fade out at the end** to how gently it should finish.
4. ### Export video
Press **Export video** (Ctrl/Cmd+Enter), then **Download video**. On a phone, Share saves it back to Photos.

## Mix or replace: which to choose

__The sound choices for adding audio__
| Choice                       | What ends up in the video                                            | Typical use                                                |
| ---------------------------- | -------------------------------------------------------------------- | ---------------------------------------------------------- |
| **Mix them**                 | The original sound and the new audio together, each at its own level | Music under a holiday clip, a voiceover over ambient sound |
| **Replace the camera sound** | Only the new audio                                                   | A noisy clip with a cleaner recording, or music only       |
| **Keep both**                | Two separate sound tracks in one file                                | Finishing the mix in another editor                        |

### Getting the levels right

Music that sits under speech usually wants to be much quieter than you first think. Start the music slider low, play a moment with talking, and raise it until the music is clearly there without competing. Each slider runs from **Off** up to about 6 dB louder than the original level, and the export keeps the mix from distorting if the two together get too loud.

## Length, timing and fades

* The new file always runs for exactly the length of the video. Sound before the video’s first frame or after its last is left out.
* Drag the audio left to start the song part-way through; drag it right to bring it in after a pause.
* **Fade out at the end** fades the added sound over 0 to 8 seconds before the picture ends. It is set to 2 seconds for music; set it to Off for a hard stop.
* Mixing and fading mean the sound is encoded once (AAC in MP4 and MOV files); the picture is still copied untouched.

If what you have is the right sound arriving at the wrong moment within one file, that is a delay rather than missing audio: [fix the audio sync](https://sync.video/fix-audio-sync) moves it in 1 ms steps.

## Doing it with your phone’s own apps

Most phones come with a video editor that can lay music under a clip, and it is worth trying first for a quick social post. The built-in editors tend to offer their own music library more readily than a song file from elsewhere, they may limit how precisely you can set the start, and some free editing apps add a watermark or ask you to sign up before saving. If you want to use your own audio file, set its start to the frame, keep the original picture quality or mix with exact levels, the browser route here does that on the phone too.

## A word about music rights

Adding a song to a video doesn’t give you the right to publish it. Commercial music in a public upload can be muted, blocked or claimed by the rights holder, and using it in paid work usually needs a licence. Music you made, tracks you have bought a licence for, and libraries that clearly allow use in videos are the safe choices. sync.video doesn’t check or change rights; it only puts the sound where you choose.

## Questions about adding audio to a video

### How do I add music to a video for free?

Drop the video and the music file here, drag the music to where it should start, balance the levels and press **Export video**. There is no account, no watermark and nothing is uploaded.

### How do I replace the audio in a video?

Drop both files and choose **Replace the camera sound**, with your new audio picked under **Use the sound from**. The original sound is left out and the picture is copied as it was.

### Can I add an MP3 to an MP4?

Yes. MP3, M4A, WAV, AAC, FLAC and Ogg files can all be added to MP4, MOV, MKV or WebM videos. The result keeps the video’s own file type.

### What happens if the song is longer than the video?

It is cut where the video ends. **Fade out at the end** fades it over the final seconds so the ending sounds intended.

### Can I start the song from the middle?

Yes. Drag the song’s bar to the left on the timeline so its middle lines up with the start of the video.

### Will this lower the video quality?

No. The picture is copied without being re-encoded. Only the sound is encoded again when it is mixed or faded.

### Can the cuts follow the beat of the song?

That is a different job: [beat sync](https://sync.video/beat-sync) cuts your clips and photos on the song’s beats and bars.

## 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)
* [ Sync a separate mic or recorder to a video Replace a camera’s scratch sound with a lav, recorder or phone recording, lined up automatically. ](https://sync.video/sync-external-audio)
* [ Beat sync video maker Clips and photos cut on the beats or bars of your own song, ready in three shapes. ](https://sync.video/beat-sync)
* [ 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)
* [ 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/)