How Can an Object Move by Less Than a Pixel Between Two Consecutive Frames? I think video is a series of picture frames. Consider a black &amp; white scenario (no RGB). A picture frame is a 2D array of pixel. Each pixel has a single color.
A pixel can't be half black or half white. It will be filled completely with one shade of color.

Consider 2 consecutive frames of video - let's say frame 1 and frame 2 .
Suppose frame 1 has a square-shaped object with coordinates $(x_1,y_1)$, $(x_2,y_2)$, $(x_3,y_3)$ and $(x_4,y_4)$ (top-left, top-right, bottom-right and bottom-left, respectively).

Now, if the object moves to the right then in frame 2 its coordinates can be $(x_1+1,y_1)$, $(x_2+1,y_2)$, $(x_3+1,y_3)$ and $(x_4+1,y_4)$ (top-left, top-right, bottom-right and bottom-left, respectively).

How is less than that possible?
The frame is 2D Grid which samples the continuous world in Discrete way.  

Leave alone video for a second.
Let's talk about taking a photo of a white paper laid on a black surface.
The photo is taken from above and let's assume there is no lens issues.
Do you expect the end of the paper to end at edge of a pixel of the camera perfectly?  

It won't.
The end of the paper will fall in the middle of a pixel.
Let's say that now this pixel (I leave out the blurring due to limited Frequency Sampling) has 70% White and 30% Black.
Now the camera moves the smallest movement and now the pixel is 30% White and 70% Black.

This is a less than 1 pixel movement.