This video illustrates various discarding/clipping techniques with a camera frustrum, using tools from the qLib asset library. (The example has some very simple geometry and animated camera.)
1. Discard geometry outside the camera view for an entire shot
We generate the camera frustrum geometry (Camera Frustrum qL SOP), then create an animated snapshot with it using the Bounds qL SOP.
The bounds node is set to return the bounding box of the frustrum animation (it shows the anim frames as a coloured guide -- I'm toggling that on/off a few times just to show that it's only a display guide, not real geometry).
Then, there's a Clip by Bounds qL SOP, which gets the input geometry and the bounding box, and _discards_ all primitives outside the box. Note that there's no clipping, just primitive deletion (which is much faster on heavy geometry).
2. Clip geometry with the camera frustrum
Next, we simply use another Clip-by-Bounds to actually _clip_ geometry with the camera frustrum (first with its bounding box, then the frustrum polymesh itself). It's pretty straightforward stuff.
TIP: Even if you're clipping, it's recommended to enable "Delete Outside". It will delete all primitives outside the clipping geo's bounding box, so the actual clipping operation will run faster.