How can I add music or audio to video without watermark?

For users comfortable with the command line, FF mpeg is the fastest way to swap audio without re-encoding the video (which preserves original quality and takes seconds). A single command copies the video stream and maps the new audio file directly into the container.

A simple command for adding music to video without watermark:

ff mpeg -i video.mp4 -i audio.wav -c:v copy -map 0:v:0 -map 1:a:0 -shortest output.mp4

Pros:

• Blazing fast
• No generational quality loss 
• supports virtually every format
• scriptable for bulk operations

Cons

• Command-line only (no GUI by default)
• Requires learning syntax