A passenger airliner traveling at the standard cruising speed of 475-500 knots (547–575 mph, 880–926 km/h) | Source
They also look like they might be traveling opposite directions, so depending on the filming airplane's speed, that makes closing speeds of upwards of 800 knots/1000 mph!
This is why Air Traffic Control, communication, and separation altitudes are so crucial—at those speeds, you'd have an instant to notice something before it hit you















