On Windows you can use the FREE
Flash Media Encoder Live 3.0 (can do either VP6 or H.264)
and
Windows Media Encoder
If you need a front end production switcher in software which can also encode to multiple sources you can use
Telestream Wirecast - $449 (test with free trial version)
It can switch between multiple cameras, do live chroma key, PIP of up to 3 sources.
encodes to
WMV
H.264 Flash
H.264 or MPEG-4 Quicktime
3GP for cell phones
If you're on Mac, Wirecast can do all the above except WMV.
BTW if you want to find out more about Wirecast I'm a "COW capo" on that forum
http://forums.creativecow.net/telestreamwirecast
