First, this is my first post in math.se, if this question is not adequate to this site, please show me where it would be fit ok ? And sorry in avance.
Yesterday I was seeing a video in YouTube in enhanced speed and tried to calculate how long the rest of the video would take in the speed I was playing. Surprisingly I got that task reaveled harder for me than I thought.
Let's say it's an hour long video and I'm seeing it in a 1.25x speed.
AFAIU the first thing I thought, is that this should be a very basic rule of three: 1 speed - 60 minutes, 1.25 - X. No... this results in 75. Longer than the video.
So I thought in another approach: 60/1,25 = 48. That's better. But 60/1,5 if 40. Shouldn't it be 45 ? because if at 2x 60 minutes should be 30. Then AFAIU 1,5x should be 45 minutes. Isn't that it?
So finally I thought in inverting it: 60/45 = 0,75 (6/8) which should be the correct value for 1,5x. And 60/30 = 0,5 (4/8) so 1,25 should be (7/8) which is 52,5 which in half between 45 and 60 minutes. Seems correct.
So in a table:
1x 1 (8/8) 60
1,25x 0,875 (7/8) 52,5
1,5x 0,75 (6/8) 45
1,75x 0,625 (5/8) 37,5
2x 0,5 (4/8) 30
But this has 2 problems. If I continue the above to slower speeds, this won't work:
0,75x 1,125 (9/8) 67,5
0,5x 1,25 (10/8) 75 <- should be 120
And even if it worked how do I create a formula to relate 1st and 2nd columns so I can calculate the value to any speed.
At this point I was so confused that I had to ask you fine people of math studies.
How do I calculate how much a video will take if I change speed ?
Thanks :)