Filter chromahold
  Turns a certain color range into gray.
    slice threading supported
    Inputs:
       #0: default (video)
    Outputs:
       #0: default (video)
chromahold AVOptions:
  color             <color>      ..FV..... set the chromahold key color (default "black")
  similarity        <float>      ..FV..... set the chromahold similarity value (from 0.01 to 1) (default 0.01)
  blend             <float>      ..FV..... set the chromahold blend value (from 0 to 1) (default 0)
  yuv               <boolean>    ..FV..... color parameter is in yuv instead of rgb (default false)

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

