[FFmpeg-user] compress security video

[Ian James]

I need to compress colour security videos for archive. Each frame is usually 95% the same as the previous frame. Switching off the audio and reducing the frame rate has not significantly reduced the file size. The image size is already at minimum. 
 The avi files are typically 1GB to 1.5GB codec WMV3 320 x 240 resolution.
 Please can someone suggest suitable profile/parameter ranges to try?
 Many thanks/