Filter fps
  Force constant framerate.
    Inputs:
       #0: default (video)
    Outputs:
       #0: default (video)
fps AVOptions:
  fps               <video_rate> ..FV.... A string describing desired output framerate (default "25")
  -start_time        <double>     ...V.... Assume the first PTS should be this value. (from -DBL_MAX to DBL_MAX) (default DBL_MAX)
  round             <int>        ..FV.... set rounding method for timestamps (from 0 to 5) (default near)
     zero                         ..FV.... round towards 0
     inf                          ..FV.... round away from 0
     down                         ..FV.... round towards -infty
     up                           ..FV.... round towards +infty
     near                         ..FV.... round to nearest


