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Proper speeding up 23.976fps footage (rule of thumb)
I’m working with a single drone shot of 3 min, shot in 24 fps. The shot is smooth and looks great in real time, but I need to speed up a portion of it.
I thought this was going to be simple … but it’s not. When I speed up the footage, it doesn’t look good any more. It’s kind of jerky, like if it was skipping frames.
When I speed it up 200%, or 400% the footage, it’s OK, but anything in-between is far from perfect. Like 150% of the speed seems to be skipping frames.
Even if I could work with 200%, the speed ramping to get there look choppy in-between. I have cache, rendered and exported the clips to make sure this was not an hardware issue.
Is there some kind of math rules I should follow to make sure everything is as smooth as possible?
I have tried with Media Composer, Resolve and Premiere and I’m having the same result. Any thought?
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4 Replies
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I think that when you shoot in 23.976fps, you should also have set the shutter speed to 1/50.
This will give you a certain amount of motion blur.
You may have to use an ND filter to be able to adjust to the correct shutter speed.Regards
Douglas
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Most NLEs vary speed by removing frames or duping frames or blending frames. All will alter smoothness of motion.
In Media Composer you can try fluid motion effect. In Premiere it’s optical flow I think.
They are processor heavy and can introduce their own issues.
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Not a Media Composer user, but chiming in to say: I would suggest a frame blending method over an optical flow-type solution; it looks a bit more like natural motion blur, and works better the faster you speed up the footage. Optical flow/morphing-type effects work better for stationary camera + moving subject; you get lots of artifacts when the camera is moving.
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One of the keys to ramping shots is to realize what frames are going to be removed.
As you said, 200 percent isn’t bad, but 150 doesn’t look as good. This makes perfect sense. If i take out every other frame, it is more likely to look smooth. If i start taking out 1 out of every 3 or 4 frames, depending on the motion involved, it will be more noticeable. Sometimes you just have to find the sweet spot, but pay attention to the math involved. You may also find quicker bursts for a shorter period of time works well. Coming in and out of speed changes will give the viewer less time to analyze the motion
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