Despite the fact you could play MIDI, it appears you have no MIDI output available. You could plug a MIDI synthetizer or even install a software one.
You must enable MIDI output by doing one of the two suggested setup steps.
After the step, just restart your browser, come back here and have fun!
With Google Chrome, you can activate the Web MIDI API in Chrome to enjoy
this player. To do so, just enable this experimental feature by
copy/pasting the following link in your address bar and checking if
the Web MIDI API is enabled:
This MIDI Karaoke player is using a very early web technology currently under standardization process.
In order to enjoy this karaoke experience under Windows and MacOSX, please download the Jazz MIDI plug-in, restart your browser and come back here!
You can choose a different MIDI output here:
MIDIWebKaraoke is an online application allowing you to play the MIDI Karaoke files (.kar) or even MIDI files containing lyrics.