The compression parameters for creating a good flv file will be different from video to video. Those are some of the important ones:
You need to get a good balance between image quality and compression, that will totally depend on your video. Transitions, camera movements and changing subjects (trees on the wind, water on a river) can be very demanding. The more still your image, the better compression you'll have.
I'll assume you have defined the size of your image. For the web 15fps is a good framerate. And for a bitrate you'll need to consider your target audience. Testing is unavoidable.
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