As indicated by the video, the complete source code is published on Github. The files posted in this project make up the complete front-end and back end of the music program. Within the root directory, you will see the JS project file, the CSS style file, and the index file.
You will also find a "drums" folder that makes up the reactive sound effects in the project. Using the WAV sound file format, it has the kick and snare sounds used in the app. Other sound applications may be added or replaced in this template but they are there as an example.