Filter stereowiden
  Apply stereo widening effect.
    Inputs:
       #0: default (audio)
    Outputs:
       #0: default (audio)
stereowiden AVOptions:
  delay             <float>      ..F.A.... set delay time (from 1 to 100) (default 20)
  feedback          <float>      ..F.A.... set feedback gain (from 0 to 0.9) (default 0.3)
  crossfeed         <float>      ..F.A.... set cross feed (from 0 to 0.8) (default 0.3)
  drymix            <float>      ..F.A.... set dry-mix (from 0 to 1) (default 0.8)

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

