The latest version of my program HARMONY provides the simplest version of this. (Show up-down, from the Show menu on the score screen)

It displays a string containing the letters d u and =

d means the next note is DOWN (lower in pitch)
u means the next note is UP (hiogher in pitch)
= means the next note is the same pitch

I could elaborate this if you ever track down a full description of the system. Note that HARMONY can import tunes from abc or (simple) MIDI

(Download HARMONY from http://www.greenhedges.com )