anchor.diff:   *
    * Not packaged:
    *   aacplus avisynth cdio-paranoia crystalhd libavc1394 libiec61883
  - *   libnut libquvi nvenc opencl oss shine twolame
  + *   libnut libquvi nvenc oss shine twolame
    *   utvideo vo-aacenc vo-amrwbenc xvmc zvbi blackmagic-design-desktop-video
    *
    * Need fixes to support Darwin:
  
positive.code:     (enableFeature (xz != null) "lzma")
      (enableFeature nvenc "nvenc")
      (enableFeature (openal != null) "openal")
      #(enableFeature opencl "opencl")
      (enableFeature (opencore-amr != null && version3Licensing) "libopencore-amrnb")
      #(enableFeature (opencv != null) "libopencv")
      (enableFeature openglExtlib "opengl")
  
negative.code: , xz ? null # xz-utils
  , nvenc ? !stdenv.isDarwin && !stdenv.isAarch64, nv-codec-headers ? null # NVIDIA NVENC support
  , openal ? null # OpenAL 1.1 capture support
  , ocl-icd ? null # OpenCL ICD
  , opencl-headers ? null # OpenCL headers
  , opencore-amr ? null # AMR-NB de/encoder & AMR-WB decoder
  #, opencv ? null # Video filtering
  , openglExtlib ? false, libGL ? null, libGLU ? null # OpenGL rendering
  