Add music to a video

How Add Music to Video works

The file is read with a FileReader, rewritten in memory and offered as a download. This is why large PDFs are limited by your device's RAM rather than by an upload size limit. A 200 MB scan never crosses the network, so the slowest part is your own disk.

That is the whole architecture: static files, one script, no upload endpoint to leak or log. Close the tab and the work is gone.

Copy the picture, rebuild the sound

Adding a track does not require touching the video stream. The engine maps the existing video packets into a new file and writes a fresh audio stream beside them, which is why the job finishes in seconds and the picture is bit-identical.

That also means the output keeps the original resolution, frame rate and colour — only the audio changes.

Replace or mix

Replace drops the original audio entirely: the right choice for a phone clip with wind noise and a clean voice-over. Mix keeps both and blends them with amix, which is what you want when the original sound matters (a crowd, a musical performance) and the music sits underneath.

Volume applies to the added track only, so a voice-over at 100% and music at 20% is two runs of this tool — or one run of a video editor.

The copyright line

The tool copies what you give it; it cannot know what you have the right to use. A song from a streaming service is licensed for listening, not for re-publishing in your video — YouTube and Instagram enforce that with claims and mutes.

Royalty-free libraries, your own recordings, and tracks under a permissive licence are the safe choices. That is a legal question, not a technical one, and no encoder can solve it for you.

Good to know

• Works offline once loaded, including on flights and in locked-down networks.
• No file size limit beyond your device's own memory.
• Free to use, with no account and no usage counter.
• Results are produced locally, so they are not logged or shared with anyone.

Questions