Filter colorhold
  Turns a certain color range into gray. Operates on RGB colors.
    slice threading supported
    Inputs:
       #0: default (video)
    Outputs:
       #0: default (video)
colorhold AVOptions:
  color             <color>      ..FV..... set the colorhold key color (default "black")
  similarity        <float>      ..FV..... set the colorhold similarity value (from 0.01 to 1) (default 0.01)
  blend             <float>      ..FV..... set the colorhold blend value (from 0 to 1) (default 0)

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

