Before and after audio player

Hey there!

I've been looking for ages for a way to do this in Squarespace: a before/after player. 

All audio mixing/mastering engineers, as well as post-production houses would explode out of sheer joy if this suddenly became possible.

As seen in the image I attached, the player would start both audios (before and after files) simultaneously and use volume of each to create a crossfade.
Click on "before" and hear the "before" audio clip, while the "after" clip is silently playing. 
Click on "after" and crossfade between the two audio files, with the "before" clip playing silently.

One player would work for 2 files.

There should be a visual indicator that the buffers are full before the user triggers "play". 

Apparently this could be done with Javascript.

Is this plugin possible within Squarespace?

Thanks a lot!