libx264 performances on iOS

I was wondering whether someone has some experience using libx264 on iPhone.

How does it perform? What framerate can I expect? Will it work for simultaneous encoding & decoding (video call) or the CPU can't handle it? I'm mainly interested with iPhone开发者_运维问答 4 and above (iPhone4/iPad 2)

Are there any precompiled universal binaries I can use?