Use keys Q and A to move around the menus, ENTER to select.
Trivia
The player is ported version of the official ZX Spectrum music compo player running in MODE 1 (both were done by Mike / ZeroTeam).
The 100Hz player is achived by reading the LPEN port (0xF8) to get the current scan row and executing the player code on line 1 and line 157 (312.5/2)
Line 1 is used as the start since line 0 starts at the very left edge of the screen but the subsequent lines start in the border area so this keeps the timing consistent within the frame.