A while back CD-i member Retrostuff brought up the MIDI sound features of CD-i and hinted the CD-i title "EZ Play Piano/Keyboard" indicated it supports MIDI according to the announcements in catalogues. We wondered if this title was in the end actually released on CD-i and if it indeed supported MIDI. Well, it appeared it was available online and Retrostuff verified it doesn't. Retrostuff found out there is no MIDI support in it, even the glossary doesn't mention MIDI anywhere. There is also no mentioning of an external keyboard which might be supported. Maybe the feature was dropped... Retrostuff: "I also wen't through the files with a hex editor, no hits on "midi", "serial", "port". If you want to have a look, this is the full (TOSEC) name: E-Z Play Today Keyboard - Now Anyone Can Learn To Play Keyboard! (1994)(Philips)(EU). It's also in MAME."
The Green Book mentions MIDI as an extension that requires additional hardware and drivers. The only units with these extensions are 182, 60x, 615 and 670. None of them has MIDI. Unless, there is a mystery MIDI extension card for the 182/60x series. But the CD-i players do play Compact disc MIDI, but only the CD-DA und CD+G portions, see the table below.
[Thanks, Retrostuff, TwBurn]