Microsoft Expression Encoder 4 Screen Capture?

So after testing a few useless screen capture softwares I downloaded microsoft expression encoder 4 screen capture. The problem is that it puts out massive screen capture video files. On a 15-20 sec screen capture it produces a 17.4MB file. And here is the confusing part when I choose a lower birate but same frame rate the video is choppy and unwatchable but I have to select 30000kbps opposed to like 500kbps for it to produce a smooth video. Does tweaking the frame rate/quality rate and also bitrate produce smaller file sizes or am do I have to find another screen capture software that captures a decent video quality with audio and average file size?