Question: Is it possible to preview and capture with ffmpeg?

Answer: Yes, it is possible. You can use the following command line in order to capture & preview your video from the INOGENI.
>> ffmpeg -f dshow -rtbufsize 1000000k -s 640×480 -r 30 -i video=”1714-INOGENI 4K2USB3″ -an -c:v libx264 -q 0 -f h264 – | ffmpeg -f h264 -i – -an -c:v copy -f mp4 file.mp4 -an -c:v copy -f h264 pipe:play | ffplay -i pipe:play

Replace the device names by the ones listed when you issue the following command:
>> ffmpeg -list_devices true -f dshow -i dummy

in 4K2USB3ffmpeg Tags: 4K2USB3