[MEncoder-users] How to detect B frames

[Gary Mort]

I have a bunch of videos coming from some unknown program that mencoder
is having trouble converting to Flash

What I'm wondering is if there is a way to analyse the videos and detect
if the videos have B frames in them?  I'm not concerned where this
analysis is done, I can download the programs to my own local system and
run an app to check, I just need some way to determine if the video is a
bad candidate for Flash conversion to begin with or not.