What is Add Audio to Video?

Add Audio to Video lets you merge a separate audio file with a video. Replace the original audio track entirely or mix a new track on top — ideal for adding music, voiceovers, or sound effects to silent footage or replacing low-quality recorded audio.

The tool runs FFmpeg compiled to WebAssembly so the video and audio stay on your device. Replace mode strips the original soundtrack and substitutes yours. Mix mode keeps both, with independent volume sliders for the original and the new audio and an offset control that slides the new track forward or back by fractions of a second. A loop toggle automatically repeats short audio until it covers the full video, fade-in and fade-out sliders smooth the start and end, and audio trim handles let you keep only the section of the track you actually want.

How to use

1. Upload your video file (MP4, WebM, MOV) and the audio file (MP3, WAV, OGG) you want to add.
2. Pick replace or mix mode, set volumes and offset, then add fade in/out, trim the audio range, or enable loop if your track is shorter than the video.
3. Process the video and download the result with the new audio track embedded.

When to use

• Replacing the wind noise on a drone clip with a licensed music bed before posting.
• Dubbing a voiceover onto a screen recording where the original mic audio was too quiet.
• Mixing background music under an interview without erasing the speaker's voice.

Result

A content creator uploads a drone footage MP4 with wind noise and an MP3 background music track, sets 'replace audio' mode, and downloads the final video with clean music instead of wind noise.

FAQ

Will the video re-encode and lose quality when I add audio?

It depends on the output format. If you keep the source container (or pick MP4 or MOV for an MP4/MOV source), the video stream copies through losslessly and only the audio is re-encoded. Choosing WebM, or converting between incompatible formats, re-encodes the video, which is slower and can slightly reduce quality. In mix mode the original and new tracks are always blended into one fresh audio track.

Can I add a song that's longer than the video?

Yes. Use the audio trim sliders to pick the exact section of the song you want — set the start and end points and only that window will play under the video. If you do not trim, the extra audio is cut at the video's duration on export.

How do I skip the intro of my soundtrack?

Drag the audio trim start slider forward by the number of seconds you want to skip. For example, set start to 2 seconds and the audio will begin two seconds into the song. The audio offset slider does the opposite — it delays when the audio kicks in inside the video.

Why does my MOV file fail to process?

FFmpeg.wasm handles MP4, WebM, and most MOV containers, but some MOV files use Apple-specific codecs (ProRes, Animation) that the wasm build doesn't include. Re-export the clip from your editor as H.264 MP4 and it will work.

How long does processing take and is anything uploaded?

Processing happens locally in your tab; nothing uploads. A 30-second 1080p clip with a fresh AAC encode typically finishes in 5–15 seconds depending on your CPU. Mixing two tracks takes a few seconds longer than a pure replace because the audio is decoded and re-rendered.

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