My DVDs appear blank when I record directly from a DVD video camera, why is this?

I have a video camera which records directly onto a DVD which is inserted in to the camera itself. The recording has definitely worked, because I can play it back on the small screen on the camera. However, when I put the DVDs into a DVD drive, they appear blank. Does anyone have any idea why?

When it records onto the disc, is it converting to MPEG4? Or AVI? MPEG2? Can you just explore the disc and see what format the video is in?

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