[russellsprouts]

Looking at the world download, it's using powered rails and observer blocks as a solid state storage.

There are only brief glimpses in the video, but here's what that looks like: https://imgur.com/a/AkOAzgF

The 14 left-right powered rail tracks are the music channels. Each vertical slice is a tick of music, and they are grouped into 9, the max length of a powered rail signal. The presence of an observer block underneath the rail indicates a note. The whole machine appears to be 128 x 14 bits. It has a serial read interface.

In more detail:

From the bottom of the image to the top you see:

- A row of redstone blocks, pistons, and redstone wire.

- A row of repeaters facing north

- A row of repeaters facing west

- An observer facing north

- 14 east-west powered rail/observer wires, sending signals to the east.

- In a layer underneath the east-west observer-rail wires, alternating columns of rails and redstone wire facing north-south. (Not visible in the picture)

- (A mirror image of the bottom)

The west facing repeaters control the current read location. The machine sends a signal until they all turn on, then waits until they all turn off, then turns them on again, etc. When one of the repeaters toggles between on and off, the north-facing observer above it sends a pulse. The pulse travels upwards in the north-south rail (in the invisible lower layer), and then if an observer is present, the signal is sent east along the east-west line for the channel.

The bottom two rows form a pause mechanism. The redstone block, piston, redstone wire row is an instant repeater line. When the north-facing repeaters are turned on, they will lock the west-facing repeaters in whatever state they are in. Using instant wire ensures the pause will happen immediately.

The whole system is mirrored at the top since the north-south rails in the lower layer can only send a signal up to 9 blocks. With read signals coming from both sides, this design could support up to 18 channels.

One last detail -- one column of music is read every 2 redstone ticks, so most of the repeaters are set to a 2 tick delay. However, the signal for a channel must be repeated using an observer every 9 blocks (adding a 1 tick delay), so the first repeater in each 9 block section is set to 1 tick. This compensates for the delay.

EDIT: I originally stated that there were 14 channels, but I overlooked that it's double-layered, and that there's a similar quad-layered system on the other side. There are 50 channels in total.

[mastazi]

Thank you, that was a fantastically detailed explanation! I didn’t realise that there was a world download in the video description, thanks for pointing that out!