The Piano Roll feature is now available in Midi Sandbox! It is an extension of the pre-existing Piano widget, which now has some new settings. If you are familiar with Synthesia, this new feature is sort of the reverse of that, since the notes travel upwards and respond to your midi input in real time.
Comment below if you are interested in having a Synthesia-like mode that reads a midi file and has the notes travel downwards, which some people like to use to practice new songs. If there is enough interest, I will prioritize it over some other features I have planned.
Learn more: https://midisandbox.com/
P.S. The song snippet from the video is 7pm from Animal Crossing: New Leaf. I'll have a separate video coming out soon with the full song, including a link to the template with the sheet music.