You’re much better off using a hardware converter for this. Both BlackMagic and AJA make the converters. Also at least one model of the Decklink HD and the AJA Kona 2 feature on-board up and down conversion. I own the Kona 2 and it has a really nice up-converter built in. I also own the Panasonic 1200A DVCPro HD deck which does an even better up conversion internally.
Walter Biscardi, Jr.
Creative Genius, Biscardi Creative Media
https://www.biscardicreative.com
Now in Production, “The Rough Cut,” https://www.theroughcutmovie.com
“I reject your reality and substitute my own!” – Adam Savage, Mythbusters