Video Playback Not Working

I’m starting a film score project (this will be the first I’ve scored in Cubase, I recently switched from Cakewalk Sonar because that program was so buggy and I heard that Cubase was more reliable)
I received the video file from the editor. The codec is h.264 MPEG-4 AVC (Part 10) according to VLC player.
It’s a 10 minute film and the file is under a gigabyte.

When I import it into Cubase and try to play the video file back, it lags like all get out. It basically shows me still frames and in order to see the next still frame I have to pause playback and press play again.

At first, my project session’s frame rate didn’t match, so I changed from 30 FPS to 23.98. That did NOT fix the issue. What am I doing wrong here?