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60fps / 150% / 25fps - Please Help!

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  • 60fps / 150% / 25fps - Please Help!

    Hey everyone!
    I've encountered a math drama here that I'm unable to solve. Situation is the following:

    For a musicvideo we've shot a couple takes where the song was played back at 150% speed which the Singer matched with his mouth movements. These shots were done in 50fps, which the Arri Alexa Mini in camera turns into 25fps which is our project framerate, so you get 50% slowmotion.

    If I take these clips and interpret them as 50fps, they are back in normal recording motion. If then I change their playback speed to 66,6% I get a subtle slowmotion while the singing is synched, since it was done at 150% speed.

    Now my problem: I've accidently recorded one of our best performance takes in 60fps instead of 50fps. I have tried numerous things, but can't synch it. When I interpret the 60fps files as 50fps, and playback in a 50fps timeline, and play them at 66,6% it's perfectly synched. But that changes when I take these clips back to my 25fps timeline obviously.

    Anybody have a clue, how I can synch my clips? At what speed would I have to play them back in my 25fps project? Dropped frames etc aren't really a problem in this edit, unsynched mouth movements obviously are the bigger issue.

    Thank you for any hints!

  • #2
    Isn't this simple math?

    But you made it very complicated by playing the song at 150% while shooting at 50%.
    This should have been 200% and 50% or 150% and 75% to make sure you don't need to use 1/3 or 2/3s which never translate into a exact digit (because the 3s and 6s go on forever: on short clips not a real issue, on longer takes the image might drift. Besides that you now always end up with interpolation of non existing frames).

    Anyway, the math:

    50/66,6% = 60/x

    (x needs to be the number that has the same relation as 50 and 66,6% have)

    x = 60/(50/66,6) = (60x66,6)/50 = (60/50)x66,6 = 1,2x66,6 = 79,92%

    Beware: 66,6666666666x1,2 = 79,9999999992
    The more precise the 2/3 is applied the further the 2 moves back behind the komma.
    So check what will give you the best result: 79,92%, 79,99% or 80%