Filter acrossover
  Split audio into per-bands streams.
    Inputs:
       #0: default (audio)
    Outputs:
        dynamic (depending on the options)
acrossover AVOptions:
  split             <string>     ..F.A.... set split frequencies (default "500")
  order             <int>        ..F.A.... set order (from 0 to 2) (default 4th)
     2nd             0            ..F.A.... 2nd order
     4th             1            ..F.A.... 4th order
     8th             2            ..F.A.... 8th order


