I am trying to create a boat explosion in front of two people for which i have shot the boat scene(without people) and two people converstaion seperately. Then I have created the exoplosion in after effects. Now I need to join these two videos and make the explosion appear in front of those people. What best can i do to achieve this. I have tried rotobrushing the people scene, but takes too long and leaves me with rouch edges.
I hope my question is clear. Please suggest me to get what i want ?
if you want the explosion to appear to be between the people and the boat then you need them on different layers. It sounds like you starting down that path but your production planning and execution was lacking.
Rotobrush or rotoscope by hand is probably your only option unless there is some way to generate a procedural matte or color key all or most of the shot with the people in the scene. A screenshot or sample frame from the shot of the people would give us an idea of the easiest way to create the matte.
Here are some resources on rotoscoping by hand. Scott Squires has the best explanation of the technique ever. Be sure and also watch part 2 of Scott's tutorial. Here's my short and quick explanation of a very workable solution.
There are lots of resources for Rotobrush, which can do an amazing job in skilled hands on the right kind of footage. Just type Rotobrush in the Search Help field at the top right corner of the After Effects project window and check out those tuturials.