Custom Blender Camera Shape? Is it possible to have a custom Blender camera shape? 

Like when rendering, the camera image outputs as a "triangle" shape? Or a polygon shape? 

Is there a trick to making a custom picture shape without actually rendering a rectangle or a square? 

The reason I am wondering is because this tutorial shows how to do it in OBS studio. So it might be possible to do in Blender.

If you know an answer, please share. I would really like to know.
Your rendered video will always be rectangular.
But you can add a mask over it, using the compositor


Create a black and white image using Blender/Photoshop/whatever
Add an RGB node, using the Mix node
Connect your BW image into the FAC input


How to connect a mask in compositor.
The RGB node changes the background color.