Here are a number of videos about the Oito Line, organized by season. These are from the Green Nova YouTube channel. They are extremely well done, essentially professional level production.
JR East operates about two-thirds of the line, from Matsumoto to Minami-Otari, JR West operates the remaining distance to Itoigawa.
Use the gear icon on the video’s toolbar to select English subtitles.
Winter
Spring
Early Summer
Autumn, parts 1 and 2
English Wikipedia page: https://en.wikipedia.org/wiki/Ōito_Line