The Delta Time is simply a standarized "clock time", which should be always be 1Hz or 1tick/1second. Some clocks can be to fast or too slow so a precise Rolex watch will show the exact delta time while a cheap one will lie a bit...
The CPU's are referred to as clocks (for eg. the overclocking). Depending on their "clock rate" some can even be over 5Ghz, so they can generate 5,000,000,000 "clock beats" per second. If you do not use the delta time in your video player, your computers clock will frames of the video 5Bil x faster then it should. So it needs to be downscaled to a human-friendly time measurement unit. Would You use miles to measure the height of an ant - You can, but why would you?
Older games for Windows 95, didn't use the delta time but were scaled for the cpu's at that time. If you load a 25 year old game into a new computer wont be able to play it, as it was meant to be used on an Intel 80386 or something similar which had the clockrate of 40Mhz. So the game would play 125x faster on the new PC with 5GHz clock.
Read about the deltatime and the clock rate on Wikipedia, and before you script anything which has a time constant keep in mind that if it is meant for different CPU's you always have to use the Delta Time. :)