Before revision:  However, prior pretraining work has been limited to only instructional videos , a domain that, a priori, we expect  to be relatively "easy:" speakers in instructional videos will often reference the literal objects/actions being depicted.
After revision:  However, prior pretraining work has been limited to only instructional videos ; a priori, we expect to be relatively "easy:" speakers in instructional videos will often reference the literal objects/actions being depicted.