Walking through walls effect!

I want to copy a sequence from the Edgar Wright/Simon Pegg film The World's End.

In the shot the camera travels from left-to-right across a room then through the wall and into another room.

I have two clips in the can, these both travel from pressed against the wall, across a room, and then pressed against the opposite wall.

I would like to be able to move clip 1 sideways out of the frame, with a black vertical bar making up the wall and clip 2 following as if the camera has moved through the wall into the next room (in clip 2).

The black vertical bar would be moving between the two clips.

I hope that makes sense.

Does anyone know how to do this?

Sure, easy. When clip 1 gets to the wall, you'll have to keyframe the Position X parameter to keep it moving across and out of the frame in the same direction and speed. You'll keyframe clip 2 the same way to bring it into the frame. Most of the time this is shot while panning past an actual doorway. Then you'll keyframe your black bar graphic across the frame in the same manner. Keeping everything timed correctly will be the only tricky part.

I've done this before, and I'd recommend you actually photograph a dark door frame, a black bar won't look like a door frame. Then in Pixelmator (or Photoshop if necessary) simply delete everything to each side of the door frame in the photo, keep a blank layer below it for your alpha (or fill it in with black). It'll be more realistic.

You're going to have to line up the door frame photo with the very edge of both clips, too. Count the number of frames you have to move Clip 1 out of the frame. Then you know to keyframe the other elements in the same manner.

OR, you could create a custom Compound Clip, that is wide enough to fit both clips, plus the door frame photo. Line them up in that, side by side. Then you only have to keyframe the Compound moving across the frame (an old FCP 7 trick).