Add audio to video online — add music, a voiceover, or replace the soundtrack. The video stays untouched (no re-encode), no watermark.
AI-powered audio review & delivery for voice production teams
Drop your video here or click to browse
MP4, MOV, M4V, WebM, MKV or AVI
Drop the music or voiceover here or click to browse
MP3, WAV, M4A, AAC, FLAC or OGG
Files are processed securely and auto-deleted — no account needed. See our Privacy and Terms.
Muxes audio onto your video — the video is never re-encoded.
Want to remove the current sound first? Use Mute Video. Need the audio out of a clip instead? Try Extract Audio from Video. Finished file too big? Run it through the Video Compressor.
Need a voiceover to add? Record one in VoiceDeck and drop it onto your cut here.
Add a video and an audio file, choose Replace or Mix, and download the MP4
You just recorded a clean voiceover, or licensed a piece of background music, and now you need it on the video — over a silent screen recording, a muted product demo, a slideshow export or a client's rough cut. That is exactly what this tool does: upload the video, upload the audio, and it muxes the sound onto the picture and hands back an MP4. No timeline, no editor to install, no account to create.
What sets it apart from a full editor is what it doesn't do to your video. The video stream is stream-copied — carried into the output untouched — so the picture is never re-encoded, there is no quality loss, and there is no second-generation compression. Only the audio is encoded, to AAC at 192 kbps. Because nothing is re-rendered, the job is fast even for long or high-resolution clips, and the file you get back looks identical to the one you put in.
There are two ways to add audio, and the right one depends on whether you want to keep the sound that is already on the video.
| Mode | What it does | Use it when |
|---|---|---|
| Replace soundtrack | Drops the video's existing audio and uses your new track as the only sound | The video is silent or its sound doesn't matter — dropping a voiceover onto a screen recording, or a music bed under a montage |
| Mix over existing | Keeps the original audio and lays the new track on top | You want to keep the dialogue or ambient sound and add music underneath, or layer a voiceover over existing sound |
If you pick Mix but the video has no audio of its own, there is nothing to mix against, so the tool automatically falls back to Replace and tells you. In Mix mode you can also set how loud the new track sits relative to the original — handy for tucking a music bed quietly under a voice.
Many online "add audio" tools quietly re-encode your whole video, which costs time and throws away a little quality every pass. This tool uses ffmpeg's -c:v copy, which copies the existing video stream straight into a new MP4 container and only touches the audio. The result is lossless picture and a quick turnaround.
There is one trade-off to know about. Copying the video stream only works when the source codec can live in an MP4 container — H.264 or HEVC, which covers the vast majority of files. If your video uses an unusual codec that can't be copied into MP4, the run fails rather than silently re-encoding and breaking the lossless promise. The fix is simple: run the clip through the Video Compressor first to convert it to a standard H.264 MP4, then add your audio here.
The output is always the length of the video, and your audio is fit to it. If the audio is longer than the video, it is trimmed to match. If it is shorter, the end of the video is silent in Replace mode, or only the original soundtrack plays after your track ends in Mix mode. This version does not loop a short track to fill a long video — the audio plays once and the remainder follows that rule. (Per-second offset and fade controls are planned for a future update.)
Video in: MP4, MOV, M4V, WebM, MKV or AVI. Audio in: MP3, WAV, M4A, AAC, FLAC or OGG. Out: always an MP4 with AAC audio. Because the video is only copied (not transcoded), the size and length limits are generous: without an account you can use a video up to 200 MB and 20 minutes and an audio file up to 50 MB; a free account raises that to 500 MB / 60 minutes of video and 100 MB of audio.
Your files are processed securely and auto-deleted after the job — nothing is kept, and you don't need an account. Working in VoiceDeck? Record or generate a voiceover there, then drop it straight onto your client's video here.
Upload your video and your music file above, choose Mix over existing to keep the original sound or Replace soundtrack to use only the music, then click Add Audio to Video. You get back an MP4 in seconds — the video itself is copied, not re-encoded, so the picture quality is untouched.
Upload the video and the new audio track, leave the mode on Replace soundtrack, and run it. The old audio is dropped and your new track becomes the video's only sound. The output length matches the video, so a longer track is trimmed and a shorter one leaves a silent tail.
No. The video stream is stream-copied (-c:v copy) — carried into the new MP4 without being re-encoded — so there is no quality loss and no extra compression. Only the audio is encoded (to AAC at 192 kbps), which is why the run is fast even for large files.
Yes — choose Mix over existing. Your new track is laid over the video's existing audio instead of replacing it, and you can set how loud the new track sits relative to the original. If the video has no existing audio, the tool falls back to Replace automatically.
The output is always the length of the video. If your audio is longer, it is trimmed to fit. If it is shorter, the end of the video is silent (Replace) or only the original soundtrack plays after your track ends (Mix). The audio is not looped to fill a long video in this version.
Bring video as MP4, MOV, M4V, WebM, MKV or AVI and audio as MP3, WAV, M4A, AAC, FLAC or OGG. The output is always an MP4 with AAC audio. If a video uses an unusual codec that can't be copied into MP4, run it through the Video Compressor first to convert it, then add your audio.
VoiceDeck adds AI-powered audio & video review and delivery for your whole team — so every file ships in spec, automatically.
