Select which video quartiles you want to report on through Column Picker:
Once your videos run, view the number of views that reach each quartile: Start | First Quartile | Midpoint | Third Quartile | Video Complete
Each quartile is unique. A video can only be associated with one quartile based on its performance.
The sum of all videos is video starts, not impressions since users can be impressed and close the video immediately in which case there'd be no quartile events.