If you are using vp8, .nxv file is already playable using common video players without converting or changing the file extension. You can also use ffmpeg or other programs to convert it (transcode) to a different video format. Example ffmpeg command to convert nxv to mp4:
ffmpeg -fflags +genpts -i your_video.nxv -r 24 your_video.mp4
At the moment, if you use h.264 codec you won’t be able to play the .nxv file with common video players or to convert it.
We have plans to provide a transcoding tool in NoMachine in the future.