Add Audio to Video
Add music or voiceovers to your video, adjust track volume, or replace existing sound completely in your browser without uploading your files to any server.
MP4, WebM, MOV, MKV, AVI, FLV, 3GP · up to 1 GB
Tips
- On your first use, the browser downloads an initial 30 MB media engine once and caches it for offline use.
- Enable the loop setting if your background audio track is shorter than the target video runtime.
- Set the background music volume between 20% and 30% if you want to keep spoken dialogue audible over the soundtrack.
How to use it
- 1 Select or drag and drop your video file and your audio file into the workspace.
- 2 Choose whether to replace the original audio completely or blend both audio streams together.
- 3 Adjust the volume slider and enable audio looping if your music track is shorter than the video.
- 4 Process and download your finished video file directly to your device.
What you should know
Adding a dedicated audio track to video footage is necessary when replacing noisy camera microphone capture or blending background music with spoken dialogue. Video containers like MP4 and WebM store video and audio streams multiplexed together. While raw video streams can often be copied losslessly without re-encoding the visual frames, combining new audio requires matching sample rates like 44.1 kHz or 48 kHz and encoding the audio stream using codecs such as AAC or Opus. Setting an appropriate audio bitrate between 128 kbps and 192 kbps ensures clear acoustic reproduction without needlessly expanding the final container file size.
This tool multiplexes your chosen audio file into your video container right inside your browser window. You can replace the original audio track completely or mix the incoming soundtrack with the existing camera sound while adjusting relative volume levels. If the audio is shorter than the video, enabling looping fills the remaining duration automatically. The WebAssembly engine processes files locally on a single CPU thread, so long high-resolution videos require extra processing time. Non-standard audio metadata, chapter marks, and secondary subtitle tracks from the original container may not carry over into the newly generated file.
Frequently asked questions
Will adding audio reduce the visual quality of my video?
When possible, the tool copies the underlying video stream directly without re-encoding video frames, preserving the original visual quality. Only the audio track is encoded and multiplexed into the output file.
Why does processing take longer on larger videos?
The WebAssembly media engine operates directly inside your browser tab on a single processor thread without server hardware. Processing speed depends entirely on your local CPU performance and video length.
Are my video and audio files uploaded to an external server?
No, all file reading, audio mixing, and video multiplexing occur locally in your browser memory. Your media never leaves your device or transfers across the network.
Guides
Articles and format references related to this tool.
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