I have SD cards in both the camera and base. My first set of cameras were Logitech Alert and they recorded continuously and then saved a few seconds prior to and after the detected activity. What you got was a complete video of what happened. If someone or something walked into the view of the camera, you got a recording of the entire scene starting with no one / nothing in the view and then the entire trip the person / critter made through the area ending with and empty scene.
I took the SD card out of the base station and looked at the contents. The base SD card contained a collection of photographs from each recording the camera had taken. It did not contain any videos. I don't understand the utility of the SD cards and the explanations for them that I have seen don't match up with what my camera is doing.
I'm a little frustrated by the lack of information and support for these cameras. There is very little help available as to how to make the cameras operate the way you want them to, etc. Between our two homes, I have at least one of every model of camera Roku sells - six cameras in total (everything but the floodlight).
I will say that the Roku cameras only record relevant action. I notice that my outdoor camera senses and brackets motion such as tree limbs swaying in the wind, but doesn't record it. That said, when it does record action, it takes 1/2 of the motion to detect it and then it only captures the final 1/2 of the motion as a video. If that is a software thing, I hope the Roku gurus tweak the system!
Like I said at the beginning of this post, my best experience with these type of cameras was the Logitech Alert system. They provided great videos showing everything that happened from beginning to end. In addition, the files were stored on your computer's hard drive and each file was depicted as a thumbnail photograph that showed the height of the activity. It was very easy to scan through a large number of files in the event there was a lot of motion detected from wind, etc.