Blackmagic Forum

Hello,

My order of operation is MediaIn>TimeSpeed (to make a freeze frame)>Tracker. As soon as I turn on match move on the track the FG over BG image shifts position. I then have to change the offset by hand to adjust back into place which isn't a perfect science. Is there a way to maintain the original position in the tracker node so It lines up with the freeze frame?

This usually happens if your reference time is not a the beginning of your clip.
Say you have a 0-100 range and you track from frame 50. The only frame where no shifting will happen is at frame 50 since that is your reference frame. All the other frames will be influenced by the track you did.
So either track from the first frame (if possible) or do the positioning of your image at the reference time.

Sander de Regt wrote:This usually happens if your reference time is not a the beginning of your clip.
Say you have a 0-100 range and you track from frame 50. The only frame where no shifting will happen is at frame 50 since that is your reference frame. All the other frames will be influenced by the track you did.
So either track from the first frame (if possible) or do the positioning of your image at the reference time.

This might be a different issue since per your example frame 50 is actually where I'm seeing the shift and it's not a time shift but a shifting of the framing. As soon as I turn on Match move the image drops about 50pixels. I can line it back up again using the x and y offset and the difference blend mode. But it seems like odd behaviour. Now this doesn't happen with my fist tracker only when I attached a second tracker after the first. Is it possible the first tracker is effecting the second?

I've attached my node tree. Each group is a paint out. Maybe somewhere in my order of operations is the issue. Thanks for your help.

You appear to be tracking at one speed and applying that same tracking data to the same media that is then at a different speed.
The Tracker will keyframe the position of the tracked pattern in your media, to each comp frame. If you then shift the time, that frames of your media occur, with regard to the comp, then the pattern you have tracked is likely to be in a different position from where it was when you tracked it originally. Since tracking produces a keyframe every frame, representing the distance travelled between every frame, if you change the timing of the media then you would need to change every keyframe, unless the pattern moves at a constant rate from start to finish. in which case you could cheat.
You need to put your Tracker after the TimeSpeed and if you change the timing, then you need to retrack
You didn't state what you were trying to achieve with the TimeSpeed.

Sorry for the confusion but the time speed is only a freeze frame. Why would that shift the center point of the track node image? I’m happy to removed the timespeed all together to see if that’s what’s effecting it. But the first node group had the identical timespeed and didn’t have this issue. Only seems to occur on the second instance. I could also replace the freeze frame with a PNG to see if that changes anything.

If this doesn’t make sense I may have to do a screen grab so demonstrate because theirs is no time shift it’s just a positional shift.

Thanks for your patience.

It depends what reference frame you have used. If the reference frame is a different frame from the freeze frame then depending on what is moving, it is highly likely whatever you are tracking has moved, otherwise you wouldn't need to track.
It's difficult to tell what is happening from a screen shot of the nodes.
If you copy your nodes and paste them into your post others will be more able to help.

I think some clarification is warranted

A Tracker has a Reference Frame. If you set the Reference in Match Move Settings (Operation tab) to "Select Time," this is the frame on which the playhead was sitting when you hit one of the Track buttons for the first time. Otherwise, by default it will be the first frame of your composition. At this frame, the transforms the Tracker will output are all zeroes, meaning that the image you apply the tracking data to will remain in its position at that frame.

The simple solution to this problem is to set Reference to Selecct Time and start your tracking at the same frame which you froze. But if you've already done the tracking, or if you need to apply the same data to more than one element that you've frozen at different points in time, then you need a way to update the Reference Frame.

The slightly more complex, but much more flexible, solution is to download TrackerPlus from Reactor, which includes a tool script called "Set Current Time as Reference Frame." Access it by right-clicking the Tracker node, and going to Script > Tracker > Set Current Time... (And in the future, use the TrackerPlus macro you just downloaded in place of the regular Tracker, as it has the script built-in, plus additional scripts to track forward and backward by just one frame at a time.)

This script will change a couple of hidden parameters in the Tracker to set the Reference Frame to the current playhead time. In the case where you need multiple Reference Frames, you'll need to duplicate the Tracker for each additional freeze frame and run the script on each of them at the appropriate frame.

I prefer to set my Trackers to FG Only and use a separate Merge node to add each element in order to reduce confusion.



I'd attach the comp itself, but trackers make it too big (and I didn't actually do the work on frame 27 anyway )

Why do you have Dutch example footage in your screenshots, Bryan?

Because the Blender Foundation's Tears of Steel project is open source, and this is a very handy shot for demonstrations of tracking. It's the same project that that curly-haired glasses guy comes from that we use for so many greenscreen demos

Ah, I see. I never managed to find the curly hair with glasses shot in the repository, since I always found navigating that specific page very complicated. For some reason I never found that specific shot, which is indeed more or less greenscreen's Marcie