Add audio to video
Put a music or voice track onto a video, replacing or mixing with whatever sound is already there. The picture is never touched.
Drop your files here
.mp4, .mov, .mkv, .webm, .avi, .m4v · up to 300 MB
How to Add audio
- 1
Add your video
MP4, MOV, MKV, WebM or AVI, up to 300 MB and an hour long.
- 2
Add an audio file
MP3, WAV, FLAC, M4A, AAC or OGG, up to 500 MB.
- 3
Click Add Audio and download
You get an MP4 with the new track, and the picture is exactly what you started with.
The picture is never touched
The video stream is copied packet for packet from the source straight into the result. No frame is decoded or re-encoded, so there is nothing for the picture to lose. Only the audio side of the job does any real work: reading the file you add, matching its length to the video, and encoding it into the container alongside the untouched video.
Replace or mix
Replace throws out whatever sound the video already had and puts the new track in its place, which is the usual choice for adding music to a silent clip or swapping a bad recording for a clean one. Mix keeps both, blended at volumes you set independently, which is what you want for a voiceover laid over quiet background footage or music added under existing dialogue. If the video has no sound of its own, mixing has nothing to blend with, so the tool switches to replace automatically.
When the lengths don't match
Trim cuts the result down to whichever of the two is shorter, which is right when you only want as much video as you have audio for, or vice versa. Pad keeps the video's own length and fills any gap in a shorter audio track with silence at the end. Loop instead repeats the audio track from the start for as long as the video runs, the natural choice for a short music loop under a longer clip.
Both files stay on your device
Both files are read and joined inside this tab: the picture is copied across untouched, and only the new soundtrack is encoded, as AAC. Nothing is uploaded and nobody asks you to sign up, and because the work costs nothing beyond your own processor, you can add sound to as many videos as you like.
Frequently asked questions
Does this change the picture quality?
No. The video stream is copied as-is, packet for packet. Only the audio side of the file changes.
What happens to the original sound?
With Replace, it's dropped entirely. With Mix, it's kept and blended with the new track at the volume levels you choose.
How do I blend both tracks?
Switch to Mix mode and set the original and new volumes independently: 100% is unchanged, and lower values turn a track down without removing it.
What if the audio file is longer or shorter than the video?
Pick Trim to cut to the shorter of the two, Pad to keep the video's length and fill the gap with silence, or Loop to repeat the audio track for the whole video.
What audio formats can I use?
MP3, WAV, FLAC, M4A, AAC and OGG, up to 500 MB.
Does the file get uploaded to a server?
No. Both files are read and combined entirely on your device, in the browser tab.
What if the video had no sound to begin with?
Mixing has nothing to blend with in that case, so the tool switches to Replace automatically, and the new track becomes the only soundtrack.
Related tools
Mute VideoRemove the sound from a video without touching a single frame of the picture. It is the fastest thing this site can do to a video file.
Change VolumeMake a file louder or quieter by a set amount, or normalise it, either to a peak level or to the perceived loudness that streaming services measure.
Video to MP3Pull the audio track out of any video and save it as an MP3 at the bitrate you choose, in your browser.
Trim VideoKeep only the part of a video you need. Pick the start and the end, and the cut lands exactly on the frame you chose.
Merge VideoJoin two or more videos into one file in your browser. Matching clips are joined without re-encoding, so quality stays identical and it takes seconds.