A lot of research about performance has been posed here. Search this forum for “Dynamic RAM” and read te larger posts.
Are you using filters or have an opacity change? Cropping, anything that would require intensive processing for every frame?
Windows 7 64-bit, ASUS P6X58D, i7 960 3.20GHz, 24.0GB DDR3, 12TB connected storage
http://www.narrowroadmedia.com