I came across this patent that was filed back in 2006:
Title: Digital scent movie projector with sound channel
Document Type and Number: United States Patent 20080043204
Kind Code: A1
A Digital Scent Movie Projector with Sound Channels. Its features include: A Digital Movie Projector, A sense of smell signal converter and a set of scent making devices. A digital movie projector uses a full frequency sound channel as its passageway to transmit sense of smell digital signal or adding a sense of smell digital signal transmission passageway besides the several full frequency and a low frequency sound channel.