Add Audio to Video Online
Add music, narration, or sound effects to an MP4, MOV, or WebM video. Replace the source audio or mix both tracks locally on your device.
Why add audio in your browser?
- Pairs one MP4, MOV, or WebM video with MP3, WAV, M4A, AAC, or OGG audio
- Replaces the original audio or mixes the new track with existing sound
- Sets a non-negative start offset for music, narration, or sound effects
- Provides independent original and added-audio volume controls in mix mode
- Exports H.264 video with 48 kHz stereo AAC audio in a compatible MP4
- Processes both source files locally without an upload, account, or watermark
Frequently asked questions
Should I replace or mix the audio?
Replace removes the source sound and uses only the new audio. Mix combines both tracks and requires the source video to contain a readable audio track.
Can the new audio begin later?
Yes. Enter a start time in seconds. Silence is inserted before the new track, and the exported file ends with the video.
What happens when the audio is shorter than the video?
The remaining video continues with silence after replacement, or with the available source audio in mix mode. The output duration follows the video.
What happens when the audio is longer than the video?
Audio beyond the end of the video is omitted. This tool does not extend the picture or create a still frame after the source video ends.
What is the output format?
The result is an MP4 with H.264/yuv420p video and 192 kbps, 48 kHz stereo AAC audio. The picture is re-encoded for consistent output across supported input containers.
Are either source files uploaded?
No. Both previews and the final encode run in your browser. Larger files use more local memory and take longer to process.
Need to arrange narration, music, and visuals on a timeline?
Tight Studio is an all-in-one screen recorder and video editor for Mac. Record, edit, and share polished demos in minutes.
- Screen recording with smart auto-zoom
- Built-in video editor with real-time effects
- AI narration and automatic captions
- One-click shareable links
macOS Apple Silicon - Free to start, no credit card required