Filter aecho
  Add echoing to the audio.
    Inputs:
       #0: default (audio)
    Outputs:
       #0: default (audio)
aecho AVOptions:
  in_gain           <float>      ..F.A.... set signal input gain (from 0 to 1) (default 0.6)
  out_gain          <float>      ..F.A.... set signal output gain (from 0 to 1) (default 0.3)
  delays            <string>     ..F.A.... set list of signal delays (default "1000")
  decays            <string>     ..F.A.... set list of signal decays (default "0.5")


