That's not really how the encoder works. All video encoders (whether you use ffmpeg or mencoder) detect the bit rate as well as the audio rate, the file type, etc. The behavior that you experienced is normal for conversions from WMV to Flash as for one, WMV uses a completely different compression algorithm than does Flash and two, vShare is setup to only do 1-pass encoding. Increasing or decreasing the bitrate doesn't really make a huge difference unless you start to change more of the options. I would search Google for some good mencoder (or ffmpeg if you are using that) settings to convert to Flash. There are hundreds of them out there. Lastly, one thing to note is that if you want really good quality out of Flash Video, you should be looking at possibly using 2-pass settings and have your server do a bit rate detection and adjust the bitrate according to the original video's quality. This will yield you the highest quality with the smallest possible file size. This is exactly how sites like YouTube do it (for their Flash Video).