A feathered mask keyframed to move with the object that crosses the screen should do the trick fairly well. Was your speed during each of the moves the same?
I'm not sure I understand your problem but I'll give it a shot...
Sounds like you set up your camera slider on, let's say, the left side of you scene, made shot one, then moved the whole rig to the right and made shot 2 and then move the rig again so that you'd get a single dolly shot over a longer distance than you could achieve with your slider.
If that's the case then the best thing to do is to take the end of shot one and lay the start of shot 2 over it with the blend mode of shot 2 set to difference. Line up the in point of shot 2 so that you get the closest match to the out point of shot 1 and then adjust the position, scale and rotation of shot 2 so that your frame is as black as possible. Make an opacity transition between the two shots and change the blend mode back to normal. Repeat as many times as needed.
Now if the speed of the shot is somewhat consistent you'll get a fairly smooth long dolly shot from several short ones. If the timing is way off then you'll need to use time remapping to try and match the speed of the shots.
If, on the other hand, you've repeated the same slider move (a dolly shot) and changed some of the elements in the scene, and you want to make all of the elements appear to be on one shot then, here again, the difference mode is your best friend for lining up the shots. Just stack shot one on top of shot 2 then adjust the timing of the move with time remap and the position scale, and rotation of the shots until the composite is mostly black. Then change the blend mode back to normal and start the roto work to combine the elements.
If you are trying to do something else try and give us a better explanation or show us the shots.
Yes it was the same speed. Is there a tutorial of this masking process somewhere? Do you know a name I could find it under?
Thanks a million for the tip
Thank you for the detailed tip on how to knock this out. I will try your first suggestion, as I think that is what I want to achieve. I will get back to you for results/troubleshooting. Is there a tutorial that could possibly support what you have suggested? Thank you for your help, I appreciate it!
Rick's explanation should work wonders depending on how your footage is shot. A simply mask as Szalam suggested could work too. Here's a very sloppy example of how it could work. I'm sure your shots were photographed with much more care, but I just made this using footage I had on my desktop for the purpose of illustrating the principal. Here I used two seperate cable shots of a bike race, but when a tree covers up the bikers in the second shot, I keyframed the mask path to block out the bikers in the first shot, so that the bikers in the second shot look like they're moving in a continuous track. Unfortunately, this example ins't totally convincing since trees are difficult to quickly mask and it doesn't help that both shots are from different angles so the sky appears in the second shot. But, if your shots are moving at the same speed and angle and the object that blocks out the shot isn't too hard to mask then you should have a much easier time with your footage:
1.) I acheived this affect simply by animating the mask path in After Effects and using the adjustable Mask Feather Tool to control the amount of feathering the mask has. Here's how it works:
A) Use the Pen Tool to draw a mask around the object you want to cover up your first scene.
B) Use the Mask Feather Tool to adjust the amount of feathering on your object especially if there's any motion blur from the camera movement. Here's a great tutorial on how to usehttp://www.video2brain.com/en/lessons/variable-width-mask-featheringvariable width mask feathering in After Effects CS6.
2.) Move the points around as you advance through the timeline and add more keyframes as you change the mask to match your footage:
3.) Finally move the edges of the mask off of the the screen so that your new scene can take over. As I said before, if your shots are moving at the same speed and angle and the object that blocks out the shot is easy to mask, i.e. something geometric with straight lines like a wall, then you should have a much easier time with your footage:
However, I do realize that your shots might be radically different than this and you may need to resort to a slightly different technique. If this is the case, please upload your shots or post screenshots and we'll have a look.
Oh wow! thanks so much for the detailed explanation and tutorials. I will working on this today and tomorrow and will use this as a guideline. If I have any issues I will upload some pictures to gove you a better idea of what I'm dealing with but after this, I am sure the task will be much easier. I will keep you informed