Filter bbox
  Compute bounding box for each frame.
    Inputs:
       #0: default (video)
    Outputs:
       #0: default (video)
bbox AVOptions:
  min_val           <int>        ..FV..... set minimum luminance value for bounding box (from 0 to 254) (default 16)

This filter has support for timeline through the 'enable' option.

