If you are using an earlier version of FFmpeg equal to or less than 3.1.5, the nlmeans filter it may not have been implemented yet, since it exists only in the most recent versions of FFmpeg. Instead, use hqdn3d or get a newer version of FFmpeg.
FFmpeg version 3.1 or higher is required for the loudnorm filter for EBU audio normalization. Versions earlier than ffmpeg 3.1 cause
No such filter: loudnormerror on the Videomass ‘Log viewing console’ and the conversion process will fail.
For VP9 encoder FFmpeg added support for row based multithreading in version 3.4, released on January 25th, 2018. As of libvpx version 1.7.0 this multithreading enhancement is not enabled by default and needs be manually activated with the
-row-mt 1switch. Note that this feature is not available if you are using an older version of the FFmpeg (eg Version 3.1.5) and should be disabled when using this encoder.