I'm working on some math education video (similar to 3Blue1Brown if you know that). Houdini seems to be a good tool to visualize some math functions in 3D. The problem is I don't know how to render it out. I don't need texture/material, I just want to render the viewport out as it is. I tried the flipbook, but it renders the viewport's background and UI altogether, and it makes the later composition work harder.

I could probably just render with Karma... but it'd be a huge waste of time. All I need is already there, right in the viewport. I just want to export it as an image sequence.

Use Opengl ROP
OpenGL render node... [www.sidefx.com]

But use png. jpg not support transparency.

If the viewport color is set to black, and the grid is off it will store an alpha from the flipbook
if you save as exr.

Use the flipbook, but change the output from Current Viewport to Beauty Pass Only. You'll get only the objects rendered without the bg, grids and handles. If you use exr, it'll also be written as HDR (fp16).