How to add a MP3 music background to a video ?
As the video source was filmed on a smartphone change the screen size
Upload the MP4 video
Upload the MP3 music file Your video will start automatically to record
Let the video play until the end and Download your video
Here is the video with a MP3 background music made with 011.video
Audio source : https://www.youtube.com/watch?v=Zcwp5v5KPrw
Video source : https://www.youtube.com/watch?v=n6ZGa2ofjSs