EditReady supports outputting Avid DNxHD and DNxHR codecs in both QuickTime and MXF formats. EditReady relies on Avid's QuickTime codecs for encoding DNX content. If you received a warning trying to output to DNxHD or DNxHR, it is because your system does not have these codecs installed.
You can download this component for free from http://avid.force.com/pkb/articles/en_US/download/Avid-QuickTime-Codecs-LE
Note: Even if you’ve got Avid installed on your Mac, installing this codec pack is necessary to enable DNxHD and DNxHR system-wide.