If it's for educational purposes, it's far more likely to be considered fair use. But there are
other factors to consider, too, like:
the nature of the copyrighted work;
the amount and substantiality of the portion used in relation to the copyrighted work as a whole; and
the effect of the use upon the potential market for or value of the copyrighted work
So if you made a mockup that used the whole composition, and you released it in a way that made it likely people would just download your mockup instead of buying the original, then you might not be able to claim fair use. But if you just mock up a portion of the original composition, and it's used in a video, a podcast, or an essay (or forum post!) that is clearly educational (or, per the statute, for "purposes such as criticism, comment, news reporting, teaching . . . scholarship, or research"), and it's not meant to replace the original work in the market, you're fine. That's why, for example, the "Switched-On Pop" podcast can play portions of pop songs, and "Every Frame A Painting" can use clips from movies.
(This is all U.S. law, but I'd imagine it's pretty similar elsewhere.)