Replace the audio in a video
Drop a video and a new audio file — the video's own sound is dropped, the new track takes its place, and you get one combined file back.
Swapping a soundtrack cleanly
Some videos are ruined by their own sound: wind battering the microphone, traffic behind an otherwise lovely shot, or a demo recorded in a noisy room. Other videos were always meant to carry different audio — a montage waiting for music, a screen recording waiting for narration. Either way the operation here is the same and total: the video keeps every frame exactly as filmed, its original sound is dropped completely, and the file you chose plays in its place. You get one combined file back, ready to share, with the video's length deciding everything.
Getting the sync right
The new audio starts at the very first frame — there is no offset dial — so any syncing happens before you load the file. The practical trick is to trim silence off the front of your audio first, and if you are recording narration, record it while watching the clip play so your pacing follows the picture naturally. Remember the length rule: audio shorter than the video leaves silence at the end, audio longer than the video is cut off. And if the original sound is mostly fine and only one moment needs to go, you do not need a replacement at all — /video-mute-tool silences just that stretch and leaves the rest.
Formats and recompression, honestly
The swap works by playing the video through once while recording it together with the new track, so the render takes about as long as the clip lasts and the result is a fresh encode — WebM or MP4 depending on what your browser records best; the download button tells you which you got. A fresh encode means a small, usually invisible quality cost. The free tier covers videos up to 1.5 minutes and 60 MB and places a small watermark on the output; a day pass or unlock removes both. One habit worth keeping: before you overwrite a soundtrack, save the original with /mp4-to-mp3 — thirty seconds of effort, and nothing is lost forever.
How the swap works
The video plays through once, muted, while the new audio plays alongside it — both get recorded together into one new file. The result follows the video's length: if the new audio is shorter it goes quiet for the rest, if it's longer the extra gets cut off.
What happens to the original audio?
It's dropped entirely — only the new audio file ends up in the result.
Is my video or audio uploaded anywhere?
Neither file leaves your computer. Your browser plays the video and the new track side by side and records the combined result locally — no server is involved at any point.
