Frame rate question

[bergqvistjl]

Hi, not sure how I would calculate this, but it would be great if i could get it to work

I have a video that is 01:18:04 long (hms) at a framerate of 23.976fps. I want to, by reducing the framerate ONLY, slow the video down so that the length is now exactly 1:31:34. What framerate would I have to use to do this. I'm sure its between 20 and 21fps (as i've done test encodes), but i'm sure there's a way to calculate an exact value (to 3 decimal places as above), can anyone help?

[Cornucopia]

You can have fractional time, but you can't have fractional frames displayed.
Real movies are shot at 24fps and then slowed down to 23.976.

So your movie is 1hr18m04s @ 23.976, but is 1hr17m59s @24fps. That means it has 112,296 frames. To play those frames in as close to 1h31m34s, you would have to have a framerate of 20.44fps (which would actually be 33.9s).
Scott

[jagabo]

Your source is 4684 seconds long and has a frame rate of 24000/1001 fps. You want it to be 5494 seconds long. So you want 24000 / 1001 * 4684 / 5494 = ~20.4411533 fps.