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
Improper fractions are the way to go!
Speed = 1/ time taken.
Speed of 5/4 means time taken of 4/5.
Think of it in terms of the new speed and not the old speed. How much slower is 100% than 150%? 100% is 2/3rds of 150%, which means that in the time it takes to watch a video at 150%, you would’ve finished 2/3rds of the video on normal speed. Therefore your time taken decreases by 33%
.25 is 1/4. 1.00 is 4/4. 1.25 is 5/4ths. .25/1.25 = 1/5th, which is 20%. I believe the problem you’re having is you’re having trouble parsing the change of denominator of the fractions, in this case it changes from 1/4th, 25%, to 1/5th 20%.
Fractions make this easier. If you play it at 5/4 speed it takes 4/5 the time.
The math is (number of frames) = (speed in frames per second) * (time in seconds)
The number of frames doesn’t change, so if you multiply either speed or time by a fraction, you have to multiply the other by the reciprocal of the fraction to cancel it out.
1.25 speed means the video goes 1/4 faster than normal, or 5/4 its speed.
Speed of a video is frames / seconds. You want the seconds (x frame, but in reality this doesn’t matter because we are using relative speed, the total frames aren’t changing)
So we spin the fraction around, 5/4 the speed becomes 4/5 the time, or 80%
1.25x speed, with cars.
Instead of 60 mph we’re going 75 mph. That 60 mile trip now takes 48 minutes instead of 60 minutes. 48/60 is 0.8 ; a 20% reduction.
1.5x would be 90 mph. For 60 miles that’s a 40 minute drive. 40/60 is 0.66 ; a 33% reduction.
When you make something play x% faster, you’re not subtracting x%, you’re *dividing* by it. So,
1 ÷ 1.25 = 0.80 = 80%
1 ÷ 1.50 = 0.67 = 67%
let’s establish some constants:
30fps video at 10 minute length is 18,000 total frames.
125% faster playback is 37.5fps — 18,000 frames / 37.5fps / 60 = 8 minutes. 8 is 80% of 10, so 20% slower
150% is 45fps — 18,000 / 45 / 60 = 6.667 minutes which is 66.6% of 10 minutes or 33% slower
In 1.25x speed, what used to take 1.25 seconds now takes 1 second to play.
A 2.5 second clip now takes 2 seconds to finish – you can imagine that 2.5 second clip split up into two 1.25-second subclips, each taking 1 second to finish under 1.25x speed.
Now imagine a 100-second video, how long would it take to play that video? Imagine splitting that video into 1.25-second sections, there will be `100 / 1.25 = 80` sections. Each of those sections would take 1 second to finish under 1.25x speed, so the video would finish in 80 seconds. That’s 20 seconds saved! The percentage change is calculated with `(new – old) / old`, so the time decreased by `(80 – 100) / 100 = -20%`.
You need to turn the fractions upside down to how you are thinking about them. The speed is in relation to x1.00 speed, so you divide _into_ 1.00.
1.00 speed is 100% speed, so
– At x1.25 speed this is 100%÷1.25 = 80%
– At x1.50 speed this is 100%÷1.50 = 66.66%
– At x2 speed this is 100%÷2 = 50%
Hopefully the last one is intuitive — if you watch something at twice is speed it takes half as long to watch.
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