What is the next song code

I want to make my button go to the next song on like spotify. I have this key on my desktop keynoard but I want to use arduino to add it to my laptop

On a PC for spotify you need to send Ctrl + Right Arrow or Ctrl + Cmd + Right Arrow on a Mac

To use the Keyboard library you will need to use an Arduino with a USB-capable processor like the Leonardo or Micro.

The USB Human Interface Device (HID) specification is here:
http://www.usb.org/developers/hidpage/Hut1_12v2.pdf

@J-M-L

and how do you do it when it is not focused on spotify

If you modify the Keyboard library to use the "Consumer" code page (0x0C) instead of the "Keyboard/Keypad" code page (0x07) you can generate the "Scan Next Track" (0xB5) button and "Play/Skip" (0xCE) button, one of which is probably what your keyboard has.

Here is someone who did exactly that back in the Arduino 1.0.5 days:
http://stefanjones.ca/blog/arduino-leonardo-remote-multimedia-keys/