Animating the merging of multiple video strips I'm trying to achieve the merging of multiple video strips like in the following 15 sec in, to 16 sec in - caravan to boat clip. I think the clip has been animated with a vertical strip. 


Could this animated area be achieved with masks in Blender? 
If so, how would I go about achieving an animated visible video area, over another video?
There are a couple ways, but I would use masks:




With a strip selected, add a mask modifier in the properties region (N) by pressing Add strip modifier > Mask. I also like to set the alpha blending to alpha over:



You can either use another strip to control the selected strip's alpha channel. You could use a scene strip to generate such a map based on the render output of a scene, or you could use an animated mask.
To create a mask, use the UV/image editor with the mode set to mask. Press &#8679; ShiftA and select the type of mask to create.
To animate it, transform it with G (translate) S (scale) and R (rotate). Insert keyframes with I.

To move the keyframes around/delete them, you can use the dopesheet in mask mode:




Unfortunately there doesn't seem to be any way to get the image editor to update in realtime at the moment, so you'll have to manually refresh it by pressing F12. For that to work, the viewed image must be set to Render result.

Result: