Filter settb
  Set timebase for the video output link.
    Inputs:
       #0: default (video)
    Outputs:
       #0: default (video)
settb AVOptions:
  expr              <string>     ..FV..... set expression determining the output timebase (default "intb")
  tb                <string>     ..FV..... set expression determining the output timebase (default "intb")


