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Old August 8th, 2007, 07:17 AM   #1
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Why am I getting pulasting slow motion?

I'm trying to get a nice fluid slow motion, but not really being successful with the 2 clips below.

Both were taken with a Canon HV20 in at 1080i, cropped and some other basic adjustments, then slowed down/rendered via Sony Vegas 7. Both have a sort of pulsating form of slow motion which is not the effect I want.

Is this the result of my Dell Dimension 8300, 2.6 ghz pc not being adequate? Or hard drive too slow for the processing? Or am I doing something wrong in the processing that causes it?

http://www.youtube.com/watch?v=7I87vgWDvOo

http://www.youtube.com/watch?v=plY19KfaW7w

Loren
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Old August 8th, 2007, 10:55 AM   #2
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Seems like you're trying to slow it down way too much.

Vegas is good enough for 25%, 33%, or 50% slowdown...

You would need a high-speed camera to capture all of the movement properly to let you slow it down adequately.

If you're using the velocity envelope, try right-clicking the clip and choosing "playback Rate" and set it to .250
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Old August 8th, 2007, 11:25 AM   #3
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Vegas does not slow motion in the way you intuitively expect. The effect is noticable at the extremes you are attempting. For better results, consider After Effects or another application with optical flow retiming.
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Old August 8th, 2007, 11:35 AM   #4
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smooth slow motion can be achieved through shooting at higher frame rates (not sure which camera you have), converting 60i footage into 30/24p footage (to keep the timeslices real...you'll lose some resolution this way) or by interpolating the frames in-between the actual timeslices. Just using the speed decrease in most editors will simply duplicate the existing frames to make it take longer to get to the next frame...frame blending will crossfade between them to help smooth it a bit, but it's still filling space with repeated information.

When my hand moves from point A to point C over the course of one frame, if you slow that to 50%, frame B needs to be created to fill the gap between frames. What you are seeing is normal...there is software that can intrepolate frame B...Shake and some of the Final Cut Studio 2 programs use "optical flow" interpolation algorithms to make frame B by analyzing A and C. Twixtor makes a program that does this too...and I think they have a windows version.

Other than that, you have to pre-plan your shoot to capture 60i footage correctly (1/120th shutter speed to get the discreet 180 degree shutter timeslices per field that people expect to see when it's slowed down)...this means more light or longer DoF (from opening the iris).

You can also shoot with a camera that supports 60p footage that can be slowed losslessly to 30p or 24p to get you smooth footage.
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Old August 8th, 2007, 01:15 PM   #5
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Thank you for your replies.

I didn't realize that Vegas would have problems with that extent of slow-motion, and since I'm still in the early learning stages of Vegas, I'm not ready to buy/learn another program yet.

Cole, I've read your reply 6 times already and each time I think I understand a little more each time, but I'm not sure the Canon HV20 can capture 60i.

Is there any possibility that the 24p/cinema mode might offer some opportunites for good slow motion, or would the 24fps frame rate just make it worse?

I understand the need for a higher frame rate to start with, but my (probably wishful thinking) is that capturing progressive in the beginning might offset the lower frame rate?

Last edited by Loren Lewis; August 8th, 2007 at 03:17 PM.
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Old August 8th, 2007, 09:07 PM   #6
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Quote:
Originally Posted by Loren Lewis View Post
Is there any possibility that the 24p/cinema mode might offer some opportunites for good slow motion, or would the 24fps frame rate just make it worse?
24p is worse. You need a high frame rate. 60 is better than 24. This could be a good start: http://en.wikipedia.org/wiki/Slow-motion http://en.wikipedia.org/wiki/High_speed_camera
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Old August 9th, 2007, 06:55 AM   #7
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I suspected that was the case, Luke, but thought I'd ask anyway.

Thanks all for helping me to gain a little knowledge, bit by bit.

Learning what Vegas 7 can do (and some of it's limitations) can be a daunting task to someone with no previous experience. I just finished the first of the 3 dvd set from VASST - setting up a portable dvd player next to the pc seemed to work well.

I have to admit.......How much respect I've gained for the amount of knowledge and skill that most of you on this group have.
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Old August 9th, 2007, 09:45 AM   #8
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I gained every spot of my knowledge the same way you just did...asking questions, lots of them. "We stand on the shoulders of giants"
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