Filter chorus
  Add a chorus effect to the audio.
    Inputs:
       #0: default (audio)
    Outputs:
       #0: default (audio)
chorus AVOptions:
  in_gain           <float>      ..F.A.... set input gain (from 0 to 1) (default 0.4)
  out_gain          <float>      ..F.A.... set output gain (from 0 to 1) (default 0.4)
  delays            <string>     ..F.A.... set delays
  decays            <string>     ..F.A.... set decays
  speeds            <string>     ..F.A.... set speeds
  depths            <string>     ..F.A.... set depths


