For long videos, midrolls are a thing, but I tend to see them as pure evil. Especially if they're placed right before a punchline of some kind or in a long relaxing music mix.
I'm perfectly fine with pre-roll and post-roll ads, but I really don't see the need for mid-rolls unless necessary to make ends meet.
Also a note: Back in the day, I used to set a mid-roll about 2 seconds before the end of the video, and a post-roll after that. If you were watching a single video and went to make a sandwich, than that was my gain, but I didn't see it as greatly if someone was watching a playlist of a series I had done.