Add or Replace Audio in Video

About Add or Replace Audio in Video

Use our Free Online Add or Replace Audio in Video Tool to easily add music or a voiceover to your videos by mixing it with the original sound, or to completely replace the video's existing audio track. If your video has no sound initially, the new audio is simply added. The final video will always match the length of your original video.

If the audio track you're using is shorter than your video, you can choose to play it once or have it loop to cover the entire video duration. Longer audio tracks will be trimmed to fit the video's length. You can precisely adjust the volume of the new audio track using a decibel (dB) scale. All processing happens directly in your browser for speed and privacy – no file uploads!

Features:

• Add or Replace Audio: Choose to mix new audio with the video's original sound or replace the original audio entirely.
• Mix with Original Sound (Add Mode): If you choose to 'Add', and your video already has audio, it will be mixed with the new track. The original audio plays at its normal volume.
• Replace Original Sound (Replace Mode): If you choose to 'Replace', the video's original audio track is removed and replaced with your new audio.
• Matches Video Length: The output video duration will be identical to your original video's duration. Audio is trimmed or looped as needed.
• Loop Option for Shorter Audio: If the new audio track is shorter than the video, you can choose to loop it to fill the entire video length, or play it just once.
• Volume Control for New Audio (dB): Adjust the loudness of the new audio track (whether adding or replacing) using a decibel (dB) scale (0dB is original volume of the new track).
• Client-Side Processing: Securely processes files in your browser using FFmpeg.wasm. No uploads required.
• Wide Format Support: Works with common video (MP4, WEBM, MOV) and audio (MP3, WAV, AAC) formats.
• Previews: Preview your original video, the new audio track, and the final video with the modified audio.
• MP4 Output: Download your video with the new/modified audio in the widely compatible MP4 format.
• Progress Tracking: See the progress of the audio processing in real-time.

How to Use:

1. Load Engine: Wait for the FFmpeg processing engine to load.
2. Upload Video: Select or drag & drop your video file.
3. Upload New Audio: Select or drag & drop the audio file you want to use.
4. Configure Audio Settings:
   • Select Audio Action:
     • Choose 'Add to Video (Mix)' to combine the new audio with the video's original sound.
     • Choose 'Replace Video's Audio' to use only the new audio, removing any original sound from the video.
   • Adjust the Volume for New Audio using the dB slider (0dB makes no change to the new track's volume).
   • If the new audio is shorter than the video, choose whether to "Play Once" or "Loop Audio".
5. Process: Click the "Process Video" button.
6. Wait & Preview: Monitor progress. Once complete, preview the video with the modified audio.
7. Download: Save your final video.
8. Share (Optional): Share a link to this tool.

Note: Processing happens entirely in your browser. Larger files or longer videos may take more time and consume more system resources. The video will be re-encoded to incorporate the audio changes.

Quick Answer

To add music or replace the sound in a video, upload the video and the audio file here, choose Add (Mix) to layer the new track over the original sound or Replace to swap it out completely, set the volume in decibels, and click Process Video. The output always matches the original video's length: audio longer than the video is trimmed, and audio that is shorter can be looped to fill the whole clip or played once. Because the volume control is in dB, you can duck background music by, say, −12 dB so a voiceover stays clearly audible. Everything runs in your browser with FFmpeg.wasm — no upload, no account, no watermark.

Common Use Cases

Adding background music to a video

Mix a music bed under existing dialogue at a reduced volume, or replace silent-clip audio entirely with a track.

Adding a voiceover or narration

Record narration separately, then mix it over the footage without needing a full editor.

Replacing audio that cannot be used

Swap out music that triggers a copyright claim, or a take with wind noise and background chatter, for a licensed or clean track.

Soundtracking silent footage

Screen recordings, time-lapses, drone shots and animations often have no audio at all; adding a track makes them far more watchable.

Dubbing into another language

Replace the original dialogue with a translated voice track of the same length.

Looping a short music clip over a long video

A 30-second loop can cover a five-minute video automatically with the loop option turned on.

Frequently Asked Questions

How do I add music to a video?

Upload the video and the music file, choose Add to Video (Mix) if you want to keep the original sound underneath or Replace Video's Audio if you do not, adjust the dB volume slider, and click Process Video. Download the finished MP4 when the preview looks and sounds right.

What is the difference between Add and Replace?

Add mixes the new track together with whatever audio the video already has, so both are audible. Replace discards the video's original audio completely and uses only the track you supplied. If the video has no audio to start with, both options produce the same result.

What happens if the audio is shorter or longer than the video?

The output always matches the video's duration. Audio longer than the video is trimmed at the end. Audio shorter than the video either plays once and then leaves silence, or loops to fill the whole clip, depending on the option you choose.

How does the decibel volume control work?

The slider is a relative gain applied to the new track only. 0 dB leaves it as it is, positive values make it louder, and negative values make it quieter. Every 6 dB is roughly a doubling or halving of perceived loudness, so −12 dB is a good starting point for background music sitting under speech.

Is my video uploaded to a server?

No. Both files are processed by FFmpeg.wasm inside your browser tab and never leave your device.

Which audio and video formats are supported?

Common video formats such as MP4, WEBM and MOV work, along with MP3, WAV and AAC audio. The output is always MP4 for wide compatibility.

Does this re-encode the video?

Yes. Changing the audio requires the file to be rebuilt, so the video is re-encoded once. Picture quality is essentially preserved but there is a small generation loss, and processing takes longer than a simple audio strip.

Can I start the music at a specific point in the video?

Not directly; the new track starts at the beginning of the video. To delay it, trim or pad the audio first with an audio editor, or split the video and process the section you want.

Can I remove all the sound instead?

Yes, use the Remove Audio from Video tool, which strips the audio without re-encoding the picture.

Related Tools

• Remove Audio from Video — Mute the clip first if you want a clean slate.
• Audio Extractor — Pull a soundtrack out of another video to reuse.
• Audio Splitter — Trim the music down before adding it.
• Merge Videos — Join clips before laying one soundtrack over them.
• Video Compressor — Shrink the finished file for upload.

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