What do you mean by FPS support? i.e. what exactly you want? And what is not ok with current support of FPS? By default it encodes with fps which was specified through VFW interface; you can change fps (not number or content of frames itself but only how fast or slow they are showed) for encoding (written into bitstream) with --fps option same as x264 cli; the only miss is that if you use VFW output (with direct file output there is no such problem) then encoding app (VirtualDub) which will make muxing (saving bitstream into AVI) wouldn't know anything about fps you specified and will mux with fps which it known for input video.
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What do you mean by FPS support? i.e. what exactly you want? And what is not ok with current support of FPS? By default it encodes with fps which was specified through VFW interface; you can change fps (not number or content of frames itself but only how fast or slow they are showed) for encoding (written into bitstream) with --fps option same as x264 cli; the only miss is that if you use VFW output (with direct file output there is no such problem) then encoding app (VirtualDub) which will make muxing (saving bitstream into AVI) wouldn't know anything about fps you specified and will mux with fps which it known for input video.