Change MP4 FPS Without Re-Encoding

[audiohominis]

Hi all.
Normally, I would de-mux, then re-mux to change the FPS of a H.264 MP4. However, a couple of days ago I came across a nifty command line snippet for mplayer (http://www.mplayerhq.hu/design7/news.html) that did just that in one step. Unfortunately, I neglected to save the text and now, for the life of me, I can't find it again.
Little help?:o
I should mention that I'm having to do this because when YAMB joins multiple H.264 streams to an MP4 file, for some reason, it takes the freedom to also change the FPS from 24 to 25 without my consent, so I would also appreciate tips on preventing the app from doing that.
Thanks

[sneaker_ger]

I don't know the mplayer command line but you could try mp4box (that yamb uses) directly using the following commandline:
mp4box -cat video1.mp4 -cat video2.mp4 output.mp4
That should join two (or more) files and not change the fps. Both Yamb and mp4box are pretty buggy (from my experience) but this simple command line should work in most of the cases.