The video clearly shows a HUD lap timer, which was used to determine the precise lap start, end, and total time. The track name 'Bedford' and vehicle 'BMW 135i' are visible on the HUD. The footage is continuous in-car POV. The estimated track length is based on common layouts of Bedford Autodrome (Grand Prix layout is ~3.8 miles or 6.1 km) and the recorded lap time, which yields a plausible average speed.