Add Audio Track to Video

Replace or layer audio on a video clip. Video stream is copied through without re-encoding; only the audio is transcoded.

What it does

Drop a video and an audio file. Pick 'Replace audio' to swap the soundtrack outright, or 'Mix with existing' to blend the new audio over the original. Optional volume multiplier and 'trim audio to video length' checkbox handle the common cases.

The video stream copies through bit-for-bit — no re-encode means no quality loss. Audio is re-encoded only to fit the target container.

How to use it

Drop video and audio — Two side-by-side dropzones. Drop a video on the left, audio on the right.
Pick mode — Replace = remove the original audio, use only the new file. Mix = sum both tracks; the new track gets the volume multiplier.
Configure and process — Volume multiplier (1.0 = unchanged). Trim-to-video keeps the audio from running past the end of the video.

When to use it

Background music over silent video

Phone recording with no audio or bad audio? Drop in a music track.

Voiceover

Replace the on-set audio with a re-recorded voiceover at a quiet location.

Soundtrack layering

Mix ambient music behind the existing dialogue without re-rendering the video.

FAQ

Will the video lose quality?: No. Video packets are copied through, bit-identical to the source.
What if the audio is longer than the video?: Toggle 'Trim audio to video length' to cut at the video's end. Otherwise the audio plays to its full duration and the last video frame freezes.