Autocrop node for Nuke. Basically just a CurveTool setup with some links and presets for autocropping.

CS_AutoBBox.tcl

set cut_paste_input [stack 0]
version 10.5 v3
push $cut_paste_input
Group {
 name CS_AutoBBox1
 selected true
 xpos -8180
 ypos -3184
 addUserKnob {20 CS_AutoBBox}
 addUserKnob {41 color T CurveTool1.color}
 addUserKnob {41 ccrange l "Intensity Range" T CurveTool1.ccrange}
 addUserKnob {41 channels T CurveTool1.channels}
 addUserKnob {41 ROI T CurveTool1.ROI}
 addUserKnob {41 resetROI l Reset -STARTLINE T CurveTool1.resetROI}
 addUserKnob {41 go l Go! -STARTLINE T CurveTool1.go}
 addUserKnob {26 ""}
 addUserKnob {41 autocropdata T CurveTool1.autocropdata}
 addUserKnob {41 numpixels l "Add Pixels" T AdjBBox1.numpixels}
}
 Crop {
  inputs 0
  box {{parent.CurveTool1.autocropdata} {parent.CurveTool1.autocropdata} {parent.CurveTool1.autocropdata} {parent.CurveTool1.autocropdata}}
  crop false
  name Crop1
  xpos -40
  ypos -322
 }
 AdjBBox {
  numpixels 1
  name AdjBBox1
  xpos -40
  ypos -298
 }
 Input {
  inputs 0
  name Input
  xpos -260
  ypos -394
 }
set N3ef0dc00 [stack 0]
 CopyBBox {
  inputs 2
  name CopyBBox1
  xpos -260
  ypos -298
 }
 Output {
  name Output
  xpos -260
  ypos -202
 }
push $N3ef0dc00
 CurveTool {
  operation "Auto Crop"
  color_panelDropped {{parent.CurveTool1_color_panelDropped}}
  avgframes 0
  channels alpha
  ROI {0 0 1920 1080}
  autocropdata {480 270 1440 810}
  name CurveTool1
  selected true
  xpos -40
  ypos -400
 }
end_group