Replace a video's soundtrack or mix music over it, processed entirely in your browser, files never uploaded.
Your files are processed locally with FFmpeg running in your browser. Nothing is uploaded; the video and audio never leave your device. First use downloads the ~31 MB engine once. Files up to 200 MB.
MP3, WAV, OGG, M4A, AAC, or FLAC.
The output ends when the shorter of the video and audio ends (-shortest), so nothing plays over black or silence at the end.
Scales your added track against the original audio, which stays at full volume.
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Footage often arrives silent (screen recordings, camera clips with unusable scratch audio, timelapses) while the perfect track sits in your music folder. This tool attaches any audio file to any video in two flavors: replace, which drops the original soundtrack entirely and installs yours, or mix, which layers your music on top of the existing audio at a volume you control.
The video track is copied bit-for-bit rather than re-encoded, so picture quality is identical to the source and processing is fast; only the audio is converted to clean AAC. Everything happens locally in your browser via a WebAssembly build of FFmpeg: no uploads, no queues, no watermarks on your audio.
Related jobs: saving a video's existing audio as a file before replacing it (Audio Extractor), removing the soundtrack without adding a new one (Video Muter), or cutting the result down (Video Trimmer).
Replace discards the original soundtrack and installs your file as the only audio. Mix plays both together (the original at full volume and your track at the percentage you set), which is what you want for laying music under recorded narration.
Both modes encode with -shortest, so the output stops when the shorter of the two inputs ends. A one-minute video with a three-minute song yields a one-minute file. Trim your audio beforehand, or accept that the tail is dropped.
Mixing needs an original track to blend with. If the video is silent, the tool detects the failure and automatically falls back to replace mode, attaching your music as the sole soundtrack; you still get a working file without starting over.
MP3, WAV, OGG, M4A, AAC, and FLAC all work. The audio is always converted to 192 kbps AAC in the output, which plays everywhere and keeps files reasonable in size. The video keeps its original container and codec.
No. The video stream is stream-copied (transferred bit-for-bit with no re-encoding), so the picture is pixel-identical to your source. Only the audio track is re-encoded, once, to AAC.