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Old July 19th, 2010, 10:19 PM   #1
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Track a moving object?

I'm relatively new to video production, so perhaps I am talking from ignorance. But I can hardly believe there isn't a simple tool to allow one to track a moving object and so fix it's location within the frame.

I'm not referring to some 'intelligent" auto stabilization gizmo (I did try the Boris Red demo, but it chokes on MTS files).

What I need is a simple way to mark the outline of an object - say a moving object that I panned badly - and then advance frames one by one as I adjust the fame position to keep object co-ordinates constant (having zoomed in enough to avoid the image border).

I got excited when I saw that Vegas had something called "motion tracking", about as I'll-named as anything could get.

I've taken to sticking clear acetate onto my screen and sketching a rough outline of the target, then steering the screen around with the panning tools to keep it stationary. But come on! I thought this would be 101. Alternatives anyone?

Thanks,
Terence

Vegas Pro 9

Last edited by Terence Morris; July 20th, 2010 at 07:04 AM.
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Old July 20th, 2010, 01:15 AM   #2
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Terence, I know what you mean. Everyone wants that when they start out but they eventually end up with a decent video head/tripod and learn to pan properly.

Currently there's no other way, it's just practise practise practise.
Cheers.
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Old July 20th, 2010, 09:14 AM   #3
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Thanks, Allen. I trust you are right - aghh! The painful truth of it :) I will certainly keep practicing.

What irks me is that this would seem a straight-forward implementation from a software POV, and IMHO a useful tool for occasions when you need to tweak-up some crucial bit of footage that cannot be re-shot.

Last edited by Terence Morris; July 20th, 2010 at 11:37 AM.
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Old July 20th, 2010, 09:43 AM   #4
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Terence,

I'll agree that shooting it well is the best solution. For post, Apple's "Motion", which is included in the Final Cut Suite, offers Motion Tracking capability. It works pretty slick as long as the motion isn't too all over the place.

Have fun!

Rob
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Old July 20th, 2010, 12:00 PM   #5
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I can't help you on the "simple" front, unfortunately, but with a little legwork you can do this for free with an AviSynth filter: YouTube - Avisynth Tracking Filter

You would need to install AviSynth, VirtualDub, and Python 2.6, and the process does involve a few different steps, but the way it works with VDub lets you drag an outline around the object you want to track, track its motion, then use a Python script to actually crop the video accordingly.

My tests haven't exactly been exhaustive, and results will no doubt vary with the type of source footage you've got, but I've had good luck with the few clips I've toyed with. Might be worth a shot if you've been unsuccessful so far.
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Old July 20th, 2010, 12:07 PM   #6
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I think this may be what you want.

mercalli
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Old July 20th, 2010, 03:49 PM   #7
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A couple of hints when panning.

This one was taught me by a cameraman who used to shoot horse races on film for early TV. If the runners are racing camera left > right for example .. keep your eye on the right side of the viewfinder and pan with them, keeping an even distance from the leader to the right edge of the screen.

Takes some practise but it works so that as they get closer, and faster, you pan evenly with them.

Works for all kinds of traffic, cars boats and trains.

And in the cams menu select + for the centre of the screen.

Cheers.
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Old July 20th, 2010, 09:25 PM   #8
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After Effects can track an object. It has a plug-in called Mocha that can do some amazing things.
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Old July 21st, 2010, 01:43 AM   #9
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Most tracking tools are intended to follow an object through the frame so you can do something with it (ie place something else over it or replace it or, etc etc etc)

But I think you're not really looking for a motion tracking tool, rather you want something to "lock on" to an object and keep it centered - ie stabilize the frame around the object

As has been pointed out, Mercali does a pretty good job of smoothing out jerky motion, but it won't "lock on" to some particular object in the frame. But then again, I don't think having something locked in the center of the frame with only the background moving would look all that great as it might seem more like - well - like you were filming a stationary object against a moving background. Sort of like riding a merry-go-round with the camera focused on a piece of the carousel. If you want people to realize that the object is moving against a stationary background, it can't be stationary in the frame.

In the early days of televised hockey, they locked onto the guy with the puck so hard that they lost all the sensation of speed that makes the sport so exciting. They've gotten a lot better at it, but I think it's an art, not a science.

Just my opinion!

By the way - if you were to post a bit of the clip someone might be able to give you advice that was more relevant to your particular problem.
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Old July 21st, 2010, 12:01 PM   #10
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Thank you to everyone for such excellent advice, and from various perspectives.

Allen, I really appreciate your panning tip and I will concentrate on doing this next shoot. I do have one technical irritation which makes things a bit trickier. The best camera I can afford at present is a Canon HF S100. One shortfall I discovered is a 1/4 second delay on the LCD image shooting at 30 fps. And I prefer 30 fps for it's low light capability. Should my videographer skills reach a level to justify it, I have my eye on the new Canon XF 300. But I happily digress.

I played with the different tools recommended, including the freeby AviSynth filter via virtual dub, suggested by Robert. This could be made to work perfectly well I think, but for myself at least it's not a workflow I would want to settle on.

In the end I found that Mercalli could do the job surprisingly well (thanks, George). Surprisingly, because the program does not use tracker points. You are right Jim, when you said what I was looking for was to lock on to an object and keep it centered, well, keep it at the same location in reference to the frame. So I was concerned that the algorithm might assume to put the panned object at the center (rarely a good aesthetic choice as you know). But in fact this was never an issue, and by twiddling the controls I could optimize the effect I was after, which as you will see is fairly subtle.

I have a couple of clips, with and without Mercalli implemented. Please remember, this is my particular jar of pickles and you might think - so what? But I have a clear sense of how and when I can use this tool, with some practice.

Also remember this is a brief panning exercise, so leave lighting and other aesthetic considerations aside. Already I see I could have used more light and a faster shutter speed to minimize motion blur. It may not be the best example, but illustrates "how" I might employ Mercalli when required.

Just so you have some context, my storyboard is a series of close-up head, eye and hand cuts as the character looks for a book, chooses it, pulls it from the shelf , flicks pages ...you get the idea. I want the smoothest pans and continuity in the final sequence, so this will challenge my manual panning skills. It's also, and perhaps primarily, an exercise in editing.

Thanks again,
Terence
Attached Files
File Type: mpg Lost For Words Seq mercalli.mpg (6.94 MB, 112 views)
File Type: mpg Lost For Words Seq.mpg (6.94 MB, 112 views)

Last edited by Terence Morris; July 21st, 2010 at 01:07 PM.
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Old July 21st, 2010, 12:44 PM   #11
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Looks good to me!

I've had good luck with Mercalli/Vegas in combination

By the way, at the end of the non-Mercalli shot it looked like the common "bounce back" you get without a good fluid head. One trick I've heard of is to use a moderately heavy rubber band to pull the handle through the pan so when you stop there is still some tension to counteract the bounce back tendency.

Just guessing - might be completely off base as I don't know what setup you were using.

But I really liked it and you did wind up with what I think of as enough motion in the frame to overcome the "stationary object - moving background" issue. Nice, in my humble opinion.
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Old July 21st, 2010, 02:18 PM   #12
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You are very observant, Jim: I hadn't noticed that bounce effect. And I definitely need to invest in a fluid head when funds allow. Thanks for general words of encouragement too!
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Old July 21st, 2010, 02:56 PM   #13
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Typically when you apply panning pressure there is an initial resistance due to friction etc that causes some degree of twist or "wind-up" in the mechanical support system - eg tripod legs can twist very slightly, etc and when you stop and remove your hand the "twist" relaxes and the camera bounces back a bit. One of the first thngs I noticed when I got a video tripod was how much less wind-up/bounce back there was.

Lower end fluid heads also exhibit some degree of bounce back due to viscosity effects etc. As the gear gets more expensive this problem diminishes. Really good tripods/heads are really expensive!

There isn't much of anything you can do about mechanical bounce back attributable to twisting as it's sort of like winding up a spring - it will return to it's original state when pressure is removed, but if the problem is caused by the fluid head, the rubber band trick can work pretty well - or just learn to hold on to the handle for several seconds after you finish the pan. Or stabilize in post like you did with Mercalli.

But as I said, I thought the stabilized version was really quite nice.
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