more automation with Cinelerra

Here's a test video I put together utilizing camera and projector automation, a png image and chroma key, courtesy of Cinelerra.

tracing a specific path using camera automation

For my Paris video, I wanted to simulate our walk of the city by panning an old map of Paris highlighted with the streets we traveled. To do this, I imported a series of large (2800x2100) still images created in Gimp and used camera automation to simulate movement. The camera automation needed to be very specific to trace our path. Thus, I had to get the X,Y coordinate pairs of each point I wanted the camera to center upon. The hurdle I encountered is that the origin of the X,Y coordinate system used in Gimp is at the upper-left hand corner of the image, whereas the origin of an image or video imported into Cinelerra is at the center of the image. So I had to do a conversion.

For an image that is 2800x2100:
(0,0) in Gimp is (-1400,-1050) in Cinelerra
(1400,1050) in Gimp is (0,0) in Cinelerra
(2800,2100) in Gimp is (1400,1050) in Cinelerra

Hence, in Gimp, all X/Y values are positive, but in Cinelerra, X and Y can have negative values.

Most of the camera automations to simulate our walk required about four coordinate pairs; hence, four conversions:
1) origin
2) first leg of walk
3) second leg of walk
4) destination

As you can see, when I wanted to change the speed or direction of the pan, the conversion of coordinates got a bit tedious. Also, I varied the movement of some of the camera automations so that not all were bezier curves, but more linear. As noted in an earlier post, this can be accomplished by displaying the X and Y camera positions and using CTRL-click on the vertices to "pull" the curves straight. This takes a little getting used to and is very time consuming. Note that there will be two sets of "pull" vertices on either side of the actual X/Y positions that you can adjust to straighten the curve slope.

But the result is quite pleasing:
ParisRoutes
55MB

smooth scrolling credits for Cinelerra

An easy way to simulate scrolling credits is to use a very long jpeg or png image and use camera automation in order to scroll from the top part of the image all the way to the bottom of it. The one issue that has been called out on the Cinelerra boards is that the default camera automation is done using bezier curves. So, what'd you'd see by taking the defaults is that the scrolling would quicken at the beginning and the end of the automation, but be somewhat linear in the middle. The steps below show how to straighten out the curves in order to make the scrolling linear from beginning to end; in other words, a constant rate of scrolling all the way through the automation. Thanks to Nicolas from Paris for the directions!

- turn on the X and Y camera position indicators in the View menu
- click on the "Generate keyframes while tweaking" small key icon in the Timeline or Compositor
- for the scroll beginning, modify the Y position of the camera, in the compositor window. You can also click the "?" icon to enter the value directly
- at the end of the scroll, click and then I go back 1 frame to edit the Y camera position again
- go back to the main window and select "Camera Y" in the view menu.
- type "Alt-F" to modify the "Camera Y" green line height to see it entirely on the video track
- click on the start keyframe while typing "CTRL" to modify the keyframe curve slope
- do the same for the end keyframe in order to get a straight line between the start and end keyframes

After tweaking the settings, the scroll speed becomes nice and linear.