How fast does a human have to move to become invisible?

[StargateMillennium]

As it's written on the tin. Let's say you have a human or a human sized object. How fast do they have to move to appear completely invisible to the human eye? No shadow. No blur. Nothing. I'll even leave a link to reference what I'm thinking of.
https://www.youtube.com/watch?v=wIHLwBtMiYI

Notice how the woman would suddenly disappear for a few seconds then we get a flurry of sparks then she'd reappear. She's supposedly running around swinging her sword during that time but is moving so fast she's completely invisible.

So how fast does she have to move? I look it up online and ppl are giving answers from a subsonic velocity to FTL.

[Rohan]

In what frame of reference are you asking from?

Are you asking in a frame of reference if the person is running or is just swinging around a blade?

Then there are other factors to take into consideration such as the the disposition of the observer, their ocular health, and mental processing speed. Also possible factors are light quality and the appearance of the observed object.

[StargateMillennium]

The observer is of optimal ocular health and mental processing speed, standing at fifteen to twenty feet away. The light factor is a bright sunny day in a green field. The observed object is a 168 cm or five foot five humanoid clad in all black.

The person is both running and swinging the blade. But I imagine the blade will hit invisibility before the person so how fast does the person have to be running to be completely invisible?

(Reference the video).

[Rohan]

If exactly as shown in the video then sub-sonic to mach speed should do it. The human brain can only process information so fast before you can even react or notice something was there. A good example is seeing a Bruce Lee demonstration in which the video is recording at 5000 frames per second and Bruce's fastest punch is 190 km/h. The speed of sound is 1,225 km/h. So if it was possible for a human like object to move that fast that would be something.

Of course this is disregarding sonic booms and visual pressure build up from such an event happening.

But if you really want to be safe, light speed it is.

[StargateMillennium]

Hmm...are there any formulas I can use? Also, there's a thought. While obviously size and coloration are a factor, perhaps speed should be thought of as angular velocity as opposed to linear velocity. I mean, the closer an object gets to you, the less it has to travel to escape a person's cone of vision which means they can afford to go slower. Which is why you can see hypersonic jets when they fly by at a certain distance.