I can't answer your question exactly, but I can say that my Athlon XP 1600 can encode DVD fomat (720x480 @ 29 fps) into DivX (same specs) at about 14 fps. You really need alot of horsepower to do it on the fly. Check out Tom's Hardware. He does alot of benchmarks using DivX and MP3 encoding. I would think a minimum of a 2.2G P4(a) would be required.