Add Audio to Video

No. The encoded picture is copied straight from your file into the new one — the frames are never decoded and re-encoded, so there is no generation loss, no softening and no change in resolution or frame rate. Only the audio track is created from scratch. That is also why it finishes in seconds: writing an audio track is a fraction of the work of re-encoding a video. If a clip arrives in a container the picture cannot be copied out of, the tool says so and stops instead of quietly re-encoding it behind your back.

Videos: MP4, MOV, WebM, MKV and AVI carrying H.264, HEVC, VP8, VP9 or AV1 — which covers phone recordings, screen captures and everything the AI video generators export. Audio: MP3, WAV, M4A, AAC, OGG, Opus and FLAC. H.264 clips come back as MP4; a WebM stays WebM so the picture can still be copied.

Yes — that is what "Mix" is for. Both tracks are kept and each has its own volume slider, so you can duck a soundtrack under someone talking. A good starting point is music 20–30% below the speech; if the words start to feel like work to follow, the music is too loud. "Replace" drops the original entirely, which is usually what you want for a silent AI clip or when the camera picked up wind.

Technically yes, this tool will not stop you — but a commercial track will get your video muted or taken down on YouTube, Instagram and TikTok, and the copyright claim follows the upload, not the file. For anything public, use music you have a licence for, or generate an original track: the link under your result opens our AI music generator with a prompt already written for a clip your length, and what it produces is yours to use.

Free, with no account, no daily limit and nothing stamped on the picture. There is no server doing the work, so there is nothing for us to meter — the mixing and the muxing happen in your own browser tab.

No. Both files are read from your disk and processed in the page. Open DevTools, watch the Network tab while you render, and you will not see a request carrying your video or your music. That also means the tool keeps working if your connection drops halfway through.

Up to 2 GB and 10 minutes for the video, and 200 MB for the audio file. The 10-minute limit exists because the mix is rendered in memory as raw audio; past that, a tab can run out of room and die mid-render, which is worse than being told up front. Anything over about 3 minutes is worth doing on a laptop rather than a phone.

It works in mobile Safari and Chrome for short clips; long ones are limited by how much memory the browser will hand a tab, so a 9:16 clip for a reel is fine while a 10-minute recording is not. Clips are processed one at a time — after a download, "Start over" clears everything and the next one is ready, and your settings for the music take a few seconds to dial in again.