There are lots of tricks to learn, but anytime you compress a movie file, you are going to lose quality. Are these for uploading to U-tube? If so, Riva FLV Encoder works pretty well. One of the reasons it works so well is that when u-tube uploads your film it converts it, and it often doesn't select the best way to compress the film. However, if your video is converted with Riva, you can select frame rate and other things for best compression. Since Riva converts it into the type of video U-tube uses, there is no need for U-tube to compress it, and it uploads as is. Every time a video is compressed and reformatted it loses quality, so this eliminates one step of compression.
Riva FLV Encoder - Free software downloads and software reviews - CNET Download.com. I learned about this on U-tube. There are technical videos that tell how to do it exactly, but it's probably easier to play with the program.