This may be a silly question, but I don't know enough about exactly what data in a file determines frame rate:

I've used Cinema Tools to conform a 25FPS clip to 23.98FPS. When I throw that conformed clip into ffmpegX, the frame rate shows as 29.97FPS. Why does that happen?

(When I drop the same clip into MPEG Streamclip, it shows as 23.976FPS. If I then export from Streamclip at 23.976--in theory outputting the same file I input--the exported file will be recognized properly in ffmpegX, and I've successfully encoded for DVD with 3:2 pulldown from that point...)

I'm interested mostly because whenever I've ignored funky/unexpected frame rates reported in ffmpegX, the output file usually stutters...

Specific advice and/or general how-frame-rates-are-recognized-by-applications info all appreciated-

Cheers,
Dan