buffer live video?

Depends on the codec and the application

If you're using Spark encoded video,you can get away with no buffer. That said, clients with insufficient bandwidth to receive the stream in real time will experience jerky playback.

If you're using VP6, I would buffer at least 0.5 seconds for smooth playback. VP6 can stutter when the buffer is zero

If you're using H.264, I would buffer at least one second. When there is less than a second or so in buffer, H.264 playback can be jumpy.

If this is not a conferencing situation (where absolute real time is a must), I would buffer a few seconds regardless of the codec.