Both .midi and .smf files are actually MIDI sounds / music, just with a bit different format with the key difference being that SMF format supports the addition of lyrics for Karaoke machines.
These files are typically not supported in standard multimedia players, or audio editors and your best bet is most likely one of the dedicated music notation software, for example MuseScore. Not only can these be used to generate music notations from various MIDI files, but often can be used to convert MIDI files as well, so midi to smf conversion this way should be doable.
Updated: October 12, 2023