A silent clip feels unfinished, and a clip with the wrong sound feels worse. This tool lets you add audio to video files in your browser: a song, background music, a voice-over or a recorded commentary. You can add sound to a video by mixing it with the sound the video already has, or by replacing that sound completely.
Pick a video and an audio file you already have, choose how they combine, and press Add audio. There is no built-in music library, so the track is always your own file, and neither file is uploaded. Read on for how Mix and Replace differ and how a track is fitted to the video.
How to add music or a song to a video
- Drop a video onto the page. You can add several, and each one gets the same audio.
- Under 'Audio file', add the song, music or voice-over. MP3, M4A, WAV, AAC and OGG files are accepted, so you can add an MP3 to a video straight from your music folder.
- Under 'The video's own sound', choose Mix with it or Replace it.
- Set 'New audio volume'. 'Repeat to fill the video' is on when the panel opens; switch it off if the track should play only once.
- Press Add audio, then save the new MP4, or download a batch as a zip.
Until you add an audio file, the tool asks you to add one first. Once it is in, its length and size show in the slot.
To add a song to a video, you need the song as an audio file, because a video file does not go in the audio slot. If the song is inside another video, convert MP4 to MP3 first and add the MP3 here. Extract audio can save it as WAV or AAC instead.
Use the preview first: the track plays in sync with the video, so you can hear where the music starts and whether it covers the speech. Nothing is saved until you press Add audio.
The new file ends in _with-audio. Your original video and your audio file are not changed.
Mix with the video's sound, or replace the audio
This is the main choice, and it decides what people will hear.
| Choice | What you hear | Use it for |
|---|---|---|
| Mix with it | The video's own sound, with your audio playing under it | Quiet background music under speech, or a voice-over added to ambient sound |
| Replace it | Only your audio. The video's own sound is removed | A clean music video, or a clip whose own sound is unusable |
Add music under the original sound
Choose Mix with it to lay background music under speech or ambient sound. The New audio volume slider changes only your track; the video's own sound stays at its own level. Start from the default 60% and lower it until the voices sit clearly on top.
This is the usual way to add music to video clips without losing what people say. If the video has no sound of its own, the panel tells you, and the new audio is all you will hear.
Replace the audio in a video
Choose Replace it when the video's own sound should go: wind noise, a hum, or music you do not want. To replace the audio in a video, the tool drops the original sound and keeps only your track, and the preview mutes the video to match. There is no need to mute the video first.
Set the volume and fit the length
Two more controls shape the result when you add audio to a video. They matter most when the audio and the video are different lengths.
- New audio volume: a slider from 0% to 100% in steps of 5. It starts at 60%. At 100% your track plays at its own level; lower it to let the original sound through.
- Repeat to fill the video: on when the panel opens. A track shorter than the video plays again and again until the video ends, and the panel tells you how many plays it takes.
- Repeat switched off: the track plays once and stops. With Replace, the rest of the video is then silent. With Mix, the video's own sound carries on.
- A longer track: audio that runs past the end of the video is cut where the video ends. The video keeps its length, and a note tells you how much is cut.
The timeline shows your audio under the video, one block for each play, so you can see where it starts and ends.
Make the sound level right
If the video's own sound is the problem, fix it first and then add your audio. When speech is too quiet to sit over music, increase video volume before you mix. When the recording is loud enough to bury your track, lower video volume first.
If you are not sure how much to change it, an audio normaliser works out the amount for you.
Background music, songs and voice-overs
Whether you add a song to a video or record a commentary, the tool works the same way. These uses come up most often.
- Background music under a slideshow or a holiday clip, set low with Mix so the original sound still comes through.
- A voice-over recorded on your phone, laid over a screen recording or a silent demo.
- A replacement for a noisy sound track, using Replace it and a clean recording of the same event.
- A looping ambient track, such as rain or a café, repeated to fill a long video.
- A narrated version of a clip in another language, where the new voice replaces the old one.
Each of these is a way to combine audio and video files into one MP4 with a single sound track. In Mix that track holds both sounds, and in Replace it holds only yours.
To merge audio and video recorded apart, such as a camera clip and a cleaner microphone recording, choose Replace it and make both start at the same moment first. For one soundtrack across several clips, merge videos into one, then add the audio once. If you drop several videos here instead, each one gets the track from its own start.
Whatever you add, make sure you have the right to use it. Free to play is not always free to publish.
Record first, then add
The tool takes an audio file, so record your voice-over with any recorder first, save it as an MP3, M4A, WAV, AAC or OGG file, and then add it here. It is the simplest way to add sound to video clips that were recorded silent, such as screen recordings.
Keep the recording a little longer than the video if you can. Extra length does no harm, because the end is cut where the video ends. If a voice-over turns out shorter, switch off Repeat to fill the video so it is not played twice.
Free, private and a little slower than most tools
Both files stay on your computer. The work runs in current Chrome, Edge or Firefox, and the server does no video work. There is no account, no watermark and no charge. Video tools do not count towards the daily limit for document conversions.
Adding audio is always one of the slower jobs, so expect it to take longer than most other tools on the site. The video can be up to 2 GB.
Plan the start of your audio: the track begins at the start of the video and cannot be moved along it. For music that comes in later, add silence to the front of the audio file in an audio editor first.
Put the right sound under your video
To add audio to a video, drop the video and your audio file into the tool above, choose Mix or Replace, set the volume and press Add audio.
It is free, it needs no account, and neither file leaves your computer.
