For this challenge, we are given a website which is playing the [2001: A Space Odyssey](https://en.wikipedia.org/wiki/2001:_A_Space_Odyssey_(film)) soundtrack.
Looking at the source code, we find the soundtrack file, `2001.mid`.
One way to hide messages in MIDI files is using the "Program change" message. This is a type of event which does not correspond to any audio, but instead is used to control device configurations.
We downloaded [stegano_midi](https://github.com/maxcruz/stegano_midi), a program which performs MIDI steganography using the method mentioned above. We made it into an executable, and used the command `stegano_midi --reveal --file=2001.mid` to reveal the message hidden in the file, if any.
Fortunately, we obtained a base-64-encoded string, which, when decoded, resulted in the flag.