As a warning. A BIG varningslarm :P
In the event of a collision, this has the capability of causing severe personal injury. If you have active headrests, this will likely interfere with their operation. If your bar extends too close to the B pillars, side impact air bag (especially the type built into the seat) operation could be compromised. So please, take note of this.
I made a similar mount for a friend (this one is for myself). He likes taking pictures of and in his car. Soooo, I'm making him a suitable mount so he can take pictures from a stable location while moving. Long exposure + night time on highway = really cool effect ;)
Step 1: Materials
4 Screws of your choice
4 Nuts to match screws
1 piece of angle iron OR aluminum to span your headrests
1 Screw to fit your camera or swivel mount
Optional: Screw Caps
Step 2: Assembly
Sand the edges of your rod to prevent cuts and scratches. Then, for ferrous metals apply nice coat of flat black -- or even textured paint to give it a nice professional looking finish. I used aluminum, and I like how it looks as-is.
Step 3: Installation
Mount Camera and Enjoy.
If you have a swivel mount -- attach it to your bar (not pictured). If not, adjusting the seat recline position will adjust the angle of your camera.
Additionally, you can modify the bar such that the camera will be outside of the vehicle.
Reminder: This can interfere with the safety devices of your car (read: side and curtain airbags et. al.). Do not leave this up permanently and use at your own risk.