I guess this reveals how fucking dumb I am. I can’t get the math to make sense in my head. If you watch at 1.25 speed, logically (or illogically I guess) I assume that this makes the video 1/4 shorter, but that isn’t correct.
In short, could someone reexplain how fractions and decimals work? Lol
Edit: thank you all, I understand now. You helped me reorient my thinking.
In: 8653
You basically divide the length of the video by the number: x/1.25 Lets say a video is one minute long: 1/1.25=0.8 That means it’s now only 80% the video length as before, thus 20% shorter.
Edit:
I dont think it’s necessary to convert these numbers into fractions, since it confuses people even more. Just think about it that way: Assume 1/x (x is the factor of the video speed) If you let x tend to zero, the video will get slower and slower, since you will divide 1 with a smaller and smaller number. (The smaller the number, the more times you can fit it into 1) You get a bigger number as the result which is your ACTUAL viewtime factor. For example: 1/0.2=5=500% So instead of 10 minutes you need 50 minutes (minutes times the factor calculated; here the factor is 5)
Likewise, if you increase x (the speed of the video) you divide 1 by a number which will get bigger and bigger. Thus, the bigger the number the smaller the ACTUAL viewtime gets. For example: 1/5.0=0.2=20% So instead of 10 minutes you only need 2 minutes to watch it.
speed=distance/time
Take a 100 minute video, the distance is the number of minutes the video is long. So if watching normally at speed=1 then, since distance=100, 1=100/time. From this we get that time=100, in other words it takes us 100 minutes to watch a 100 minute video at normal speed (duh).
Now say we bump speed to 1.25. We now have 1.25=100/time. So time=100/1.25=80, a reduction in 20%.
The reason a 25% increase in speed leads to a 20% decrease in time is because 1/1.25=0.8.
At 1.5 speed, you’re watching 1.5 seconds per real-life second. If the original video took x seconds, then the sped-up video takes (x / 1.5) seconds.
* Watch Time = x / 1.5
* Watch Time = x / (3 / 2)
* Watch Time = 2/3 x
So the watch time is 2/3rds of the original time…so decreased by 1/3.
I’m trying to explain this in a way that will be intuitive.
Think about watching a video at 1.5x speed, and that after the video ends it keeps playing just showing a blank screen. If you watch that video at the 1.5x speed for the amount of time you would normally watch, you will have seen the whole video plus half the video duration in blank screen.
Now if you consider what you watched as a whole, 33% of it was blank screen. You watched the first half of the video, the second half, then half the duration in blank screen. So of the time you needed to watch the video at normal speed you have reduced it by 33% since you can skip the blank screen time.
Imagine you have a dollar in quarters, so 4 quarters. 100% = 100 cents. So 125% = 125 cents = 5 quarters. However the new quarter is only 1 of 5 quarters, 1/5 = 20%, therefore your new quarter represents 20% of your total money now.
Now imagine you have a dollar in 50 cent coins. 2 coins. You get another 50 cent coin, increasing your money to 150% of what you used to have. However, that new 50 cent coin is one of three, so it represents 33% of your money now.
If you went 2.00 times faster, would you expect to get there instantly? No, instead, it’s half the time. When you go X times faster, you reduce the time to 1/X. So 2 times faster makes the time 1/2 what it was. 5 times faster, you’d get there in 1/5th the time. 1.25 times faster can be expressed as 5/4 times faster, and you get there in 4/5th the time, or 80%.
Consider this: It’s impossible to watch a video _infinitely_ fast. You can’t speed it up so much that it takes no time to watch it. But your sense is that increasing the speed by 25% should decrease its length by 25%, and so presumably increasing it 50% should decrease it by 50%, and increasing it by 100% should decrease its length by 100%, which would make it 0 in length, i.e instant, merely by doubling the speed.
In fact, the speed being a multiplier of the original means it can never end up at 0. If you watched a 5 minute video at 5.0x speed, you can probably intuit that it would take 1 minute to watch – saving you a cool 4 minutes. But if you double that speed again, to 10.0x you can again probably intuit that you won’t save four minutes again. In fact, you’ll only save a further 30s because doubling your speed from 5.0x to 10.0x halves the time to watch it not from the original 5m, but from the already-shortened 1m.
The moment you speed the video up, it’s no longer “1” in length but rather something smaller than 1. So any additional speed ups will be applying to something less than 1, meaning it’s not a linear relationship. This sounds very complicated, but the maths is incredibly simple:
1.0 / speed factor = Proportion of the original length
So to input your own examples, we have…
1.0 / 1.25 = 0.8
1.0 / 1.5 = 0.667
If you multiple those results by 100, you get the percentage change from the original length. And my example:
1.0 / 5.0 = 0.2 (and so if the original video was 5m long, that multiplied by 0.2 = 1m)
P.S. If anyone ever tells you that they’re going to decrease your pay by 10% but, don’t worry, they’ll then increase that by 20% next month to make up for it, you’re getting screwed for precisely the same reason!
1.25 is 5/4.
If the video is sped up 5/4, then the time to play it back will be 1 divided by 5/4, or 4/5 (80%). To watch the whole video in that time: 5/4 x 4/5 = 20/20 = 1. 80% is 20% less than 100%.
Likewise for 1.5x: 1.5 = 3/2, so duration is 1 / (3/2) = 2/3 (67%), which is 100% – 67% = 33% shorter.
The math makes a lot more sense if you use fractions instead of decimals.
Watching it at 1.25 speed means you’re watching it at 5/4 speed. To see how much time it would take, you would take 4/5th of the time, which is 80%.
Watching it at 1.50 speed means you’re watching it at 3/2 speed. The amount of time it would take (flipping the fraction) is 2/3rds of the time, which means you saved 33% of the time.
It’s sometimes easier to imagine with bigger %s.
Watching at speed X 2.0 decreases the time by 50%. Speed is 2, time taken is 1/2.
Watching at speed X 1.5 decreases the time to watch by 33%. Speed is 3/2, time taken is 2/3.
Watching at speed X 1.25 decreases the time to watch by 20%. Speed is 5/4, time is taken 4/5.
Saying +25% speed should decrease the time by 25% is like saying +100% speed should decrease the time by 100%. If that was how it worked, watching it at double speed would result in the video ending instantly.
Latest Answers