You’ve mixed MiniDV and Mpeg in the same sentence. I can only guess you have an HDV camera?
Playing an HDV tape out though the HDMI will be no better than a standard ingest of HDV material.
But lets say you have your computer with the Intensity, on location, connected to the camera, live via HDMI. You could then record the digital video straight off the camera, before it ever hit the compression hardware. The video would be as good as the camera could produce. A bit more clumsy, but you avoid the compression.