If you're talking about the .GCV codec the program uses, I believe the only way to convert those is with the in-built media player/converter. Click on "media" in the main menu. Click on the movie icon (first arrow), choose the video you want to convert then click on the exporter/converter (second arrow) and then choose either "MJPEG compressor" or "Microsoft Video 1". Clicking on "export" the program then saves as .AVI video (I don't know about the Radius Cinepak-codec),
But the videos stay in low resolution, I believe 800x432 and also the AVI codec is not ideal being very bulky. Furthermore a water mark/logo shows up at random times. So I strongly advise against using the game's video grabber but instead use an external program like f.e. OBS Studio to do the job.
EDIT: I see this was an old question, but what the hell! I reckon the info is still useful.