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30fps vs 60fps handling motion

Mar 11, 2012 10:03 PM

I have a low cost Kodak ZX5 Playsport waterproof pocket video camera that comes in handy on vacations (hiking, rafting, swimming, etc).  This camera has the ability to record in either 720p 30fps or 60fps modes. 

 

I notice when there is any motion recorded, the 60fps provides a significantly smoother look to the recording.  In comparison, the 30fps appears jittery and sometimes like a strobe effect.  For example, I recorded a test of my son jumping on the trampoline today.  60fps is relatively smooth and looks natural.  But 30fps looks jittery and unnatural, like someone moving in front of a strobe light, as if the movement is too large between frames.  I don't understand why 30fps looks so bad.  Aren't many films recorded with an even lower 25fps?  And television is 30fps (although interlaced)?  I realize film makers use techniques to lessen jitter, and I have attempted to emulate these in some other recordings, but still it seems there is more to this situation than simply camera technique.  I have seen plenty of films and DVDs of the action genre, where there is lots of character/vehicle movement recorded - and these do not look like what I am getting with the 30fps Playsport.  Not to mention, by old DV tape camcorder did not have this jitter either - and I think it recorded at 30fps (I will verify this).  Is there something else having to do with interlacing, or some kind of blurring, that makes recording devices that share 24 or 30 fps appear different in terms of how smooth motion looks?  If so, can I emulate this with some settings in Premiere or maybe After Effects?

 

I plan to edit the footage in CS5 Premiere, and am inclined to use the 60fps setting for recording because it looks so much better for any type of motion.  But if I need to reduce 60fps down to 30fps to cut a standard definition DVD, maybe 60fps is not the way to go?  Is anyone editing footage from these type of smaller camcorders, and if so what fps settings are you using, and how are you dealing with motion jitter?  I don't want to come back from vacation with a whole bunch of 60fps material and find out it was a mistake.  Thanks for any advice.

 
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  • Currently Being Moderated
    Mar 12, 2012 8:57 AM   in reply to Indio22

    I notice when there is any motion recorded, the 60fps provides a significantly smoother look to the recording.  In comparison, the 30fps appears jittery and sometimes like a strobe effect.........I don't understand why 30fps looks so bad.

     

    Just as 60 fps are twice as many frames as 30 fps, this means the video recording is updated twice as often. Think about it like this...the 60 fps recording is capturing the frames IN BETWEEN every two frames that are recorded by the 30 fps. So anything that changes between 2 frames of the 30 fps recording would be captured by the 30 fps recording.

      Aren't many films recorded with an even lower 25fps?  And television is 30fps (although interlaced)?  I realize film makers use techniques to lessen jitter, and I have attempted to emulate these in some other recordings, but still it seems there is more to this situation than simply camera technique.  I have seen plenty of films and DVDs of the action genre, where there is lots of character/vehicle movement recorded - and these do not look like what I am getting with the 30fps Playsport.  Not to mention, by old DV tape camcorder did not have this jitter either - and I think it recorded at 30fps (I will verify this).  Is there something else having to do with interlacing, or some kind of blurring, that makes recording devices that share 24 or 30 fps appear different in terms of how smooth motion looks?

     

    To your first question, yes and no. Some films are recorded at much higher frame rates than even 60 fps (portions anyway...high action stuff, anything that will be slowed waaaaaaaay down - think about the Matrix "bullet time" effect for example). But you're on the right track. Most theatrical releases are screened at 24p (24 progressively-displayed frames per second).

     

    To your second question, yes and no. NTSC is 29.97 fps but is really 60 partial frames per second (indicated as 60i). In other words, it is capturing new data every 1/60th of a second, but only HALF of the frame (because it is interlaced). So while you could say "film is 24 fps and TV is 30 fps" you would be technically correct but the difference is again between interlacing and progressive. So remember, 24p (PROGRESSIVE) is recording new video every 1/24 of a second (relatively slow) and 60i is recording new video every 1/60 of a second (relatively fast).

     

    About film techniques, YES, this is the big difference maker. In films, the camera almost ALWAYS keeps the subject framed consistently so that even if it's a car racing through the streets of San Francisco, the actual car in the frame isn't "moving" much at all...the filmmakers have kept it framed pretty much near the center the whole time. The background elements are what is primarily moving, and for the most part, you're probably not paying any attention to those background elements because they make up a smaller portion of the screen....and, well, they're the background. Go back and watch a car chase film and completely cover the center of the screen (or wherever the fast-moving subject is) and watch only the background. You'll see horrible strobing effects on all of it.

     

    Sometimes.

     

    Well, another part of it also has to do with depth of field. If the background elements are flying around at a rapid pace but they are not sharply focused (due to being behind of or in front of the focal plane of the subject), then it lessens the strobing effect substantially. With your Kodak camera, EVERYTHING is in sharp focus because of the way the lens is designed (very small lens, no depth), so the strobing effect of items in the frame is much more noticeable as motion in the frame increases. So the depth of field is another technique utilized by filmmakers to reduce strobing when shooting/displaying 24p.

     

    Thing about a movie like Blair Witch or Cloverfield. People were puking in their seats from all the strobing because it was shot "handheld-style" to give it the non-professional feel. But that's what happens when you shoot like a home video enthusiast and not like a filmmaker. It's not an insult, it's a matter of the technique.

     

    Try this....get your kid jumping up and down on the trampoline again and get up close so his face fills about 1/2 to 2/3 of the frame, and track his motion closely as he goes up then down, etc. You'll notice the strobing disappears or is lessened. That's the technique you need to use when shooting lower frame rates. Otherwise, shoot at 60p. There's no reason not to do so in most cases. AVCHD/H.264 codecs usually record constant bitrate within any given quality setting regardless of frame rate, so you're not going to see any savings on the file size. If it's sports or high motion and you don't need to screen it in a movie theatre, there's probably no reason you "must" shoot 24p.

     

    However, 24p DOES have a magical quality to it in the way it looks, but you have to follow the rules to keep everyone from throwing up when they watch "Lord of the Trampoline" on their 55" HDTV.

     
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