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Old October 16th, 2007, 01:59 AM   #1
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Can I fit a spline to the keyframes when panning?

Hi,

I'm panning across a still image and I want to change panning direction, so I insert a 'transition' keyframe at the point where I want to turn, and then a 'destination' keyframe and sure enough, the conceptual 'camera' follows the path that I've specified.

However.... at the point where the 'camera' makes the turn, it slows down, executes the turn, and then speeds up again. Fair enough, I know how to prevent this by reducing the default 'smoothness' setting from 1 to zero. Which prevents the slowdown (great!!) -- but now introduces a sharp, very noticeable, jagged turn. (Actually I assume the turn was just as jagged before, but the slowing down would have helped to hide it.)

So is there any way to fit what I think is called a spline curve around the keyframes? What I'm looking for is to make the camera 'flow' smoothly through (or around) intermediate keyframes -- I don't even care if it precisely hits them as long as it gets back on track again within a half dozen frames or so. I'm pretty sure I used to be able to do this back in Premiere 5.0(!!) so I figure there must be a way to do it in Vegas too? (I'm still using Vegas 6 btw.)

(Also btw: the various keyframe settings -- linear, fast, slow, smooth, etc -- only seem to affect the *speed* in various cryptic ways; they don't seem to exert any control over the actual (spatial) *path*.)

I'm really hoping someone can help me with this! It must come up all the time, right? And yet I can't find any previous posts about it....
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Old October 16th, 2007, 02:27 PM   #2
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Quote:
linear, fast, slow, smooth, etc
As far as I know, it's the same idea as in cross dissolves.

If you look at your cross dissolve / cross fade options, you see that there are a number of different curves available.

2- Vegas doesn't let you control splines on the motion keyframes (AFAIK). The closest you get is adding multiple keyframes and then changing smooth/linear/etc.

Also check out the manual:

Quote:
If you have two or more keyframes, you can expand the Keyframe interpolation heading and edit the Smoothness setting to adjust the smoothness of the motion.

Smoothness adjusts spatial interpolation: how motion occurs within the frame. A Smoothness setting of 0 produces linear motion from one keyframe to the next. Increasing the setting produces a curved path.

If you want to adjust temporal interpolation how motion occurs over time change a keyframe type by right-clicking a keyframe and choosing a new interpolation curve type (hold, linear, fast, slow, or smooth).

During playback, intermediate frames are interpolated to create smooth motion. For more information about keyframe animation, click here.

Use the Default Pan/Crop smoothness control on the Editing tab of the Preferences dialog to set the default Smoothness value for new keyframes.
3- In other programs you can adjust the spline controls on keyframes.

The ProType titler in Vegas lets you have spline controls on keyframes, but I don't think it can manipulate images.
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Old October 17th, 2007, 12:03 AM   #3
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Hey Glenn,

Thanks for your reply.

To get the slight digression out of the way first -- The first problem I have with those linear, fast, slow, sharp, smooth, and hold keyframe options is that in the context of cross dissolving or fading, these options are intuitively understandable, but when it comes to keyframes on a path, it's really hard for me to figure out what the y-axis represents on those small explanatory graphs. The manual calls it 'rate of animation' of the 'effect parameter'. But at the very least the graphs seem to be upside down -- that is, high values on the graph represent a small change, and low values represent a large change. Thus eg 'hold' is represented as a high value (which means 'no change') for the entire width of the graph; it doesn't switch to low until it reaches the next keyframe. The second problem I have is that it would be so great if you could choose whether to have these options apply *between* keyframes (as they do now) or *at* keyframes, ie so you could control how the curve passes through the keyframe. That would be nice because, under the present regime, if you set a sequence of keyframes to 'smooth' what you get is a smooth path *between* them and (usually) a jolting change in speed and/or direction at the keyframes themselves. All information about 'incoming' speed and direction is ignored once you hit the next keyframe, and the interpolation starts over again from scratch. Consequently, the typical result is anything but smooth!

Anyway, sorry -- I don't mean to be too whiny about this. But maybe this could be added to a wish list somewhere?

As for your points 2 and 3, yes I was afraid this might be the case. Pity :( Also I haven't had much luck with adding multiple keyframes to try to smooth out the transitions manually. All that happens is that the original problem just propagates to the new keyframes!

I do stand corrected by the manual though: The 'smoothness' control only produces that temporal easy in/easy out effect on the first and last keyframes. At all intervening keyframes, the smoothness is entirely spatial (ie the path itself is altered, not the distance between frames), so I was wrong when I said it slowed down and sped up again. In fact the smoothness parameter actually produces a spline of sorts! Sadly though it's only a rather weak, half-hearted, uncontrollable one. As things stand then, it seems that setting the smoothness value of one is probably about as good as a result as I can get. (Here's another wish-list request: it would actually be nice if the smoothness went up to 11 or whatever instead of maxing out at '1' OK, obviously these are arbitrary numbers, but it would be nice if the weighting and extent (how many frames before and after) could be adjusted -- then I could make my own splines and all would be well with the universe :)
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Old October 17th, 2007, 06:42 AM   #4
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Just a thought, Norman . . . a pretty straightforward workaround might be to use your original settings (i.e. where it causes the unwanted slow down on the turn) and then apply a velocity envlelope to try and speed up the turn as required to smooth things out.

This assumes you are happy with the spatial movement as it is and that you're just trying to correct the deceleration/acceleration aspect.

For simplicity it might be easier to render out the keyframed sequence and apply the velocity adjustments on the rendered clip.

Out of curiosity, are you doing this in 3d space or 2d?
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Old October 17th, 2007, 07:29 AM   #5
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Hey Ian,

Thanks for your suggestions.

Actually, I've since discovered that it *doesn't* in fact slow down and speed up again when it goes through an intermediate keyframe. The easy in/easy out only happens at the first and last keyframes. And the smoothness setting actually does introduce some splining around the intermediate keyframes, but unfortunately it's quite a sharp curve and there seems to be no way to make it any smoother.

It might be a good idea though to use the velocity envelope to *slow down* (as opposed to speed up) when going through a keyframe. Hmm, yeah, that might work! It won't fix the too-sharp spatial movement, but it might go a long way towards hiding it! Anyway, I'll render out the clip (I agree that it's definitely better to work on a rendered-out clip) and play around with that. Thx!

FYI, I'm actually using layers of 2d photoshop flats to fake out moving through 3 dimensions. I've got the whole setup working great -- everything except for the simple 2D panning! For some types of project, 2D flats are a cheap but effective stylistic choice that can look pretty cool. Also I don't have any 3d software ;)
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Old October 18th, 2007, 11:13 PM   #6
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Just a quick update -- tweaking the velocity envelope is indeed a pretty effective way of making the transitions appear smoother! It's not perfect but it's considerably better than I had before, so thanks again Ian for steering me in that direction.
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Old October 19th, 2007, 03:49 AM   #7
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Great, glad it's going some way toward what you wanted.

BTW, the reason I asked about 2d or 3d is that I was wondering if you were applying any 'banking' as you make the turn. That can sometimes smooth out a sharp corner.

Cheers,

Ian . . .
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Old October 19th, 2007, 04:24 AM   #8
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Quote:
Originally Posted by Ian Stark View Post
BTW, the reason I asked about 2d or 3d is that I was wondering if you were applying any 'banking' as you make the turn. That can sometimes smooth out a sharp corner.
Oh I see! I should have figured that out! Anyway, yeah, if I have time I should probably come back and see if I can get a better result using 3D tracks. The problem with that for me is that I always have a hell of a time working with Vegas' 3D interface -- and here I'd need to be doing it on multiple tracks (ie one for each 2D layer), all synched up, so it's a little intimidating. For a simpler project this would definitely be something to explore though. Thanks!
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Old October 19th, 2007, 04:29 AM   #9
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Agreed - maybe a bit too complex in Vegas. That kind of thing I tend to do in AE anyway, where you have vastly greater control over the 'camera'. Good luck with it!
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Old November 5th, 2007, 09:53 PM   #10
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Postcript -- finished 'Roach Motel' video

As a postscript to this thread, the finished project is now online. It's a 50 second, lo-fi animation called Roach Motel, and you can find it here -- http://fordfilmchallenge.telegraph.co.uk/site/

I'm afraid the website is a bit of a dog, but if you keep trying, it should load eventually(!). Once it does, then go to the 'view entries' page and look for 'Roach Motel'. The videos are in random order and there's no search option, so to find it you'll probably have to use the orange scroll bar on the right.

Also, it's a contest, so if you like it, then please feel free to go ahead and vote for it. :-)


In the end, I went back to using the Vegas-default, rather abrupt jumps in panning direction because unfortunately, even though the velocity envelope helped to smooth things out, it also introduced quite a lot of undesirable blur in some of the frames -- presumably as a result of interpolation.
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Old November 20th, 2007, 10:39 PM   #11
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Post post script...

Alas, the contest was a bust, but the video is now posted on Youtube http://www.youtube.com/watch?v=1aKVobBiaio
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