Looking for HTML5 code etc to enable user to select different audio tracks to play with video

I have a project I'm working on in HTML5 java script and css. It is designed to be wrapped up into a stand alone mobile phone app. I studied coding in various formats over 20 years ago and built multimedia websites for clients. How things have changed........in a good way on the functionality side of things with HTML5 etc

Basically the app enables a user to select a video and can also select up to 4 different background audio files to play in sync with the video. If it is possible to select different up to 4 video backgrounds to play behind the main video as well, would be a bonus. All the videos I have created are produced with an alpha channel. There are 11 individual videos the user can select from.

To keep the file sizes small all the videos are all 6 seconds in duration in Mp4. The audio tracks sounds are Mp3's. The video and audio will need to loop in sync continuously until the user stops the play.

I have spent a good deal of time looking for appropriate code that will enable this process to happen, but have had no success. I have found snippets on this site for looping and controlling video etc, that I have experimented with but implementing the audio and video background user select functions has escaped me.

I am hoping that one or more of you good folks on this site can assist me with producing this code and providing any additional thoughts and suggestions that could be useful for my project.

Many thanks in advance Michael