http://tomthinks.com/rodent.html
That guy made that animation in maya and added it on top of his video. Is it possible to do that with blender? if so, how?
thanks.
Yes, but you’ll have to rotoscope which is a fancy way of saying “masking”. This is usally done via a pen tool and bezier curves or by painting directly on an image’s alpha channel. You basically load background images into the 3D viewport for reference and go from there. Don’t know if you noticed the cheesy background visible through the doorway, but that should have given you a hint as to what was going on.
Look in the tutorials saction for something like compositing CG into live footage or stills.
In the above example, you are dealing with three locked shots. So you will need to create 3 matched camera in blender that match the angle of the orginal shot video.
Then build up fake geometry that will catch the shadows you want to convey as well as do some of the masking for you.
Place your animation in the scene and render from each camera to get the footage you need.
That kind of work is rarely done in a single app. Compositing will have to take place. You can use blender for this or After effects or final cut.
How am I going to place my animation inside the video i recorded? that was basically my main question to start with 
thanks.
This guy was actaully cheap and didn’t use camera movmement. LOL
If you are planning to use motion (which you should) visit colin’s tracking tutorial at: http://www.peerlessproductions.com/tuts/pages/Icarus.html
Anyways I’ve answered part of the question here: http://blenderartists.org/forum/showthread.php?t=84675
If you have part of the video that overlaps the 3d object you would create a 3d object in the same exact place (also animate it if it actaully moves) and enable the ENV button in the textures. This will make the area not render and so the video from the behind will be seen.
In this scene where the monster walks behind the triangle thing, I had to rebuild the roof he walks on to delete his other leg, for shadows and to delete the moment where he actaully goes behind:
Also animation wise you will need to recreate everything the character interacts with, even if you are not going to use it in the final render. It will KILL you if you try to guess what is located where in 3d space unless you recreate it. You’ll need to pick a point, like in the image below, the corner of the building and try to match the 3d grid so it maches up with the axis of the building. If you use icarus for tracking they have (some what hard to use, hard to get used to system) to do that.
In this scene the monster interacts with objects, and so his head/teeth had to be deleted as he goes behind the object, I had to recreate that corner.
Everything you want a shadow to be cast upon, floor etc. you would need to build. You would need to enable the “Only Shadows” button in the materials, also bring the alpha level down. (The alpha level will determine the transparency of your shadow.)
You will also need to create an area lamp with the following settings:
I’ve enabled the “Only Shadow” button because I didn’t want the lamp to affect the lighting I set up for my character. The lamp in this case is only a “Shadow Maker” Also make sure you have “Ray” enabled in the render menu.
(monster steps on the steps, so had to recreate the steps for shadow reasons.)
See all those dots? Those were created by a program called icarus. Since the scene involved zooming in (or camera movement), the program identified certian points and tracked as they moved. The data was than imported into blender and I was able to add a 3d door opening inside the statue. AND the door moved along with the scene since the 3d camera in blender matched that movement.
If you actaully want to see the finished project, take a look here: (some of the scenes are missing shadows, I had only a month to finish the project and shadows take forever to render!!! Tracking a few seconds of a scene can take hours!) http://calvin.sdlfk.org/calvin/monster.zip (sorry link down)
Enjoy 
If you need any help once you begin on your journey, be sure to ask for help. I am always here.
Some tips:
- Always use a tripod. (Free motion is VERY hard to track.)
- It is much easier to set up your camera (the whole grid thing I was talking about above) if the scene contains a cube. Somewhere where you can pick a point at (90 degree angles) and match each XY and Z with. (For me it was easier because I had cube/buildings to work with.) What professional do, (King Kong, Star Wars) they place objects within scene that have 90 degree angles and than later mask them out in post.
Is Icarus really that slow? I’ve played with voodoo several times and it tracks fairly quickly. I know that a lot of people have complained about voodoo on these forums, but I haven’t read any complaints concerning the current version. It does’t like ATI graphics cards though. Any mouse actions while it’s tracking will cause it to crash and even brought down my graphics card drivers once.
I tried voodoo, it kept crashing. It requires too many resources. One time that I did get it to actually track a scene it turned out horrible. (I’ll have to try the newer version)
As far as Icarus being slow, it really depends how many tracking points you use and your system. I was able to track the same scene that took me 4 hours to track, 1 hour at a friends computer.
I’ve only played with voodoo just for the sake of the experience. I think the crashing may have something to do with direct x and graphics card drivers not liking each other. I have to turn hardware accelleration nearly all the way down (disable all direct draw and direct 3d accellerations, as well as all cursor and advanced drawing accellerations) on this new computer or blender crashes. Go figure.