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Re: Gorpro Hero 4 Black, 120fps, CC 2014

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Jeff Pulera
Re: Gorpro Hero 4 Black, 120fps, CC 2014
on Dec 22, 2014 at 3:47:14 pm

Hi Todd,

From what I've read in the past, some cameras that offer "overcrank" will actually record one second of video as two seconds on the card so that the slow-motion does play back "automatically". In other words, maybe you record 60 frames per second, but it gets written to the card as two seconds of 30fps video.

With GoPro, one second is one second, but there are 120 frames in that second of video. Premiere is intelligent enough that if you put that 120fps video into a 30p or 60p sequence, the playback speed still seems normal... it just skips the "extra" frames. A 120p clip in a 30p sequence will just play every fourth frame, which should look no different than a clip actually recorded at 30p.

However, if you do a Speed Change, Premiere also has the intelligence to utilize the extra frames from the 120fps clip rather than interpolating frames (blending/repeating frames).

For instance, you have a 30p clip in a 30p sequence and apply 50% slow-mo, each frame gets played TWICE, so it looks a little choppy. But if you put a 60p clip in that same 30p sequence and apply 50%, Premiere takes two seconds to play one second of source clip, playing each frame once, so it should look silky smooth. You have 60 frames, and playing them at 30fps takes two seconds.

Your 119.88fps divided by 5 = 23.976, so to use ALL of the 120 frame per second for slow mo, you would use 20% slow motion (one-fifth speed) and one second of raw video will take 5 seconds to play back, using every frame. Of course, 24p always looks a little choppier because of the lower frame rate, so it may not provide results as smooth as 30p for instance. In a 30p sequence, you would use 25% speed to use all 120 frames, or 50% would use every other frame (60 of the 120 frames).

For the 23.976 sequence, stick with multiples of 20, like 40 or 60 for instance for best results. If my math is correct, 40% will use every other frame and should also provide smooth results. 60% would use every third frame, 80% every fourth frame.

Hope this all makes sense (and that I got it right!)


Jeff Pulera
Safe Harbor Computers

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