Filter acrossover
  Split audio into per-bands streams.
    slice threading supported
    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 9) (default 4th)
     2nd             0            ..F.A..... 2nd order
     4th             1            ..F.A..... 4th order
     6th             2            ..F.A..... 6th order
     8th             3            ..F.A..... 8th order
     10th            4            ..F.A..... 10th order
     12th            5            ..F.A..... 12th order
     14th            6            ..F.A..... 14th order
     16th            7            ..F.A..... 16th order
     18th            8            ..F.A..... 18th order
     20th            9            ..F.A..... 20th order
  level             <float>      ..F.A..... set input gain (from 0 to 1) (default 1)


