Here's everything about media saving in Virtual.ink
To internally record your light-painting work, press the "b" key from the live view. Depending on the specs of your computer, you'll be able to record from a few seconds to a few minutes. For longer performances or to offload your computer, it is better to save from an hdmi recorder (Atomos) or from a second computer. Tip: the lower the resolution, and the longer you'll be able to save internally
Internal saving means that you'll get the mp4 from the software and it is going to be available in the gallery.
For specific duration recording, use the corresponding box in the "Action" menu from the dashboard.
Single frames can be saved at any time. When you are in record mode, the files are saved within your actual session. However, if you are not recording, each file is creating a new session (a new element in the gallery). Tip: use the "e" (export) key from the keyboard or the export button from the live-view / web-remote.