Hello,
in "includes/upload_definitions.php", find:
$mime_type_match['mid'] = array("audio/x-midi", "audio/mid", "audio/midi");
add after:
$mime_type_match['kar'] = array("audio/midi", "music/x-karaoke");
in "templates/your_template/media", create a file called "kar.html", with this code:
<!-- Template file for KAR Audio Files -->
<embed src="{media_src}" type="audio/midi" hidden="true" autostart="true" loop="true" height="1" width="1"></embed>
{media_icon}<br />
At the end, in "templates/your_template/icons", add the kar icon, you will find in attachment (for administrators and developers, it would be better to have png icons, as gif format copyright is really boring).
Once done, kar files will work as midi files.