The source code is everything you'll find when checking out the Video.js git repository. This includes all the source files and any tooling necessary to build a production ready version of Video.js, as well as useful development tools such as sandboxed examples.

A lot of the root source directory is JSON configs for various package managers because, Internet. Most likely the important things you're looking for will be in src/ and build/. src/ contains all of the source files for both the player JS and the base skin, while the build/ directory contains various grunt tasks as well as the primary build file, grunt.js.