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60fps / 150% / 25fps / Math issues

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Lucas Fiederling
60fps / 150% / 25fps / Math issues
on Apr 29, 2017 at 12:32:17 pm

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!

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Chris Wright
Re: 60fps / 150% / 25fps / Math issues
on Apr 29, 2017 at 5:17:04 pm

I hope this is right. confusingly AE and premiere are exact opposites in handling speed changes. 50% AE speed up, but 50% premiere slows down!!! haha...

3 ways I see.

1. 25fps/60fps is 0.4166666666 or 41.66666666% slower recording speed. you then speed up to 141.6666666% to get "normal speed" again. Final slow playback matches 66.6% subtle slow motion from top part
2. or just set clip speed to 94.44444444%.(141.66*66.6) if playback is 100%
3.or just interpret clip as 10.416666665 fps.(25*0.4166666) with playback 66.6% or interpret 6.944444 fps with playback 100%(this last one seems wrong to me)

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Lucas Fiederling
Re: 60fps / 150% / 25fps / Math issues
on May 4, 2017 at 4:03:20 pm

Hey, thanks for the help! Non of these work/make any sense to me though :(

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Blaise Douros
Re: 60fps / 150% / 25fps / Math issues
on May 4, 2017 at 5:42:25 pm
Last Edited By Blaise Douros on May 4, 2017 at 5:44:48 pm

I think you're over-complicating this.

Drop your 59.94 clips onto your 25p timeline, without interpreting the footage to 50p. If the camera interpreted your 59.94 shots as 25p, then interpret them back to the speed at which they were shot, i.e. 59.94. Slow them down to 66.6% just like you did with the 50p clips. Premiere will take care of the rest. You'll probably want to turn on Frame Blending rather than Frame Sampling as the interpolation method, to keep the frame jumps from getting too obvious.

See, you're confusing a simple time issue with a framerate issue. You need your footage to be 66.6% slower than it was shot regardless of the framerate, because that's the speed that will sync with the music.

What you really should have done is shoot your footage at 37.5 fps (which is the native 150% speed of 25 fps). Or, speed up the music to 200% and shoot at 50p. That's how you'd get a lossless framerate conversion. You'll be getting frame jumps no matter if you shot it at 50p or 59.94p, because you didn't plan your workflow correctly from the beginning.

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Lucas Fiederling
Re: 60fps / 150% / 25fps / Math issues
on May 4, 2017 at 6:24:22 pm

Hey Blaise!
Thanks for the response. You definately made some glass shatter for me!
The 37,5fps hint is great and makes all the sense in the world.

Then again it works pretty good already/ no obvious framejumps with 50p/150%/25 project rate, except on that take in question where we rushed back from a slowmotion scene to catch that perfect and rare light moment, and I was so rushed I switched back to 3,2k and forgot it natively sets to 60p on the alexa.

I also had tried the method you explain after some back and forth confusions, but on top of everything I know now that at parts the performance is simply off synch, which made me think my translation was the problem. That's by the way why I do 150% and not 200% - cause already on 150% it gets hard for the singer to lypsynch everything without being too awkward. In this case though, without reference audio, it took me quite some time to realize that in this one out of 15 performance takes, he sings the layered audio in the background of the song, instead of his normal verses.

Murpheys law all over this one take - luckily the rest of the project was a walk in the parc ☺
Greetings and thanks a lot,

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