anchor.diff:      /**/(fflag "--disable-libnpp" "3.1")
       #"--${boolEn (mmal != null)}-mmal"
       /**/"--disable-mmal"
  -    "--${boolEn nvencExtLib}-nvenc"
  +    "--${boolEn (nvidia-video-codec-sdk != null)}-nvenc"
       "--${boolEn (libva != null)}-vaapi"
       "--disable-vda" # darwin
       "--${boolEn (libvdpau != null)}-vdpau"
  
positive.code:     # Undocumented before 3.0
      (fflag "--${boolEn (libgcrypt != null)}-gcrypt" "3.0")
      (fflag "--${boolEn (gmp != null)}-gmp" "3.0")
      "--${boolEn (gnutls != null && !opensslExtlib)}-gnutls"
      "--${boolEn (stdenv.cc.libc != null)}-iconv"
      (fflag "--${boolEn (jni != null)}-jni" "3.1")
      "--${boolEn (ladspa-sdk != null)}-ladspa"
  
negative.code:     # Undocumented
      (deprfflag "--${boolEn (dcadec != null)}-libdcadec" null "3.0")
      (fflag "--${boolEn (libebur128 != null)}-libebur128" "3.1")
      (deprfflag "--disable-libfaac" null "3.1")
      (fflag "--${boolEn (fdk_aac != null)}-libfdk-aac" null)
      (fflag "--${boolEn (fontconfig != null)}-libfontconfig" "3.1")
      #"--${boolEn (flite != null)}-libflite"
      /**/"--disable-libflite"
  