Imagine you type "HELLO" in 2+1/2 seconds and that you take a screen shot with each keystroke.
______________ ______________ ______________ ______________ ______________
|H | |HE | |HEL | |HELL | |HELLO |
| | | | | | | | | |
| | | | | | | | | |
| | | | | | | | | |
|______________| |______________| |______________| |______________| |______________|
screen shot #1 screen shot #2 screen shot #3 screen shot #4 screen shot #5
Imagine that you then make a movie of the screen shots. The following diagram
[H___________][HE__________][HEL_________][HELL________][HELLO_______]
uses symbols: [H___________] [HE__________] [HEL_________] [HELL________] [HELLO_______], to represent the 5 screen shots as frames. Time runs left to right. Underline characters are added to the symbols to equalize their durations and to enhance their presentation.
+----------------------------2.5 seconds----------------------------->
import pictures: (H___________)(HE__________)(HEL_________)(HELL________)(HELLO_______) ...2pps
NOTATION: [2pps]2fps
+----------------------------2.5 seconds----------------------------->
export frames: [H___________][HE__________][HEL_________][HELL________][HELLO_______] ...2fps [note 1]
[note 1] The actual key closures occur at the [ moments rather than throughout the [____________] times. Those moments are denoted by PTSs (presentation time stamps) in metadata for each frame.
+---------------------------------2.5 seconds---------------------------------->
import pictures: (H_____________)(HE____________)(HEL___________)(HELL__________)(HELLO_________) ...2pps [note 2]
NOTATION: [2pps]4fps
+-------------1.25 seconds------------->
export frames: [H_____][HE____][HEL___][HELL__][HELLO_] ...4fps [note 3]
[note 2] Notice that this diagram's '2.5 seconds' and the prior diagram's '2.5 seconds' look different. They are the same 2.5 seconds, but their seconds-per-texipix scales differ. Time scales are generally not shown in diagrams. Instead, per-second rates are denoted. If needed, texipix characters can be counted and the counts used to calculate seconds-per-texipix but seconds-per-texipix is usually unimportant.
[note 3] Because the camera shots were at 2pps and because the frame rate is 4fps and because there's one picture per frame and because only frames have PTSs, the movie is played back with a x2 speedup.