My fireplace is flanked by 24" depth bookshelf niches.
I want to install a flat-panel TV so that it is flush with the fireplace, so 24" off the back wall.
I'm aware that "full extension" mounts exist that can extend to that full distance. I will probably use one of these to mount the TV. However, I want to be able to pull the TV out into the room (past being flush with the fireplace) and then rotate it toward the viewer. So the combined total distance will be greater than what one on these mounts can offer.
I'd instead like to install a permanent horizontal "pillar" cantilevered off the back wall of the bookshelf. This will bring the TV forward about 20"; the rest will be covered by the extension mount. The near-closed position of the mount will have it flush with the fireplace.
Rough idea below. Studs on the left, pillar, mount, TV.
How should I construct this cantilevered pillar on which I will mount the TV?
The pillar needs to extend forward 20 inches or so. The weight of TV + accessories will be 100-150lb. The mount may extend the TV forward another 18".
Smaller/simpler is better, rather than constructing a large box or major bracing. Metal or wood materials will be considered. The back wall is standard American drywall over 2x4 studs.