Filter extractplanes
  Extract planes as grayscale frames.
    Inputs:
       #0: default (video)
    Outputs:
        dynamic (depending on the options)
extractplanes AVOptions:
  planes            <flags>      ..FV..... set planes (default r)
     y                            ..FV..... set luma plane
     u                            ..FV..... set u plane
     v                            ..FV..... set v plane
     r                            ..FV..... set red plane
     g                            ..FV..... set green plane
     b                            ..FV..... set blue plane
     a                            ..FV..... set alpha plane


