Flip HD VBR MP4 joining? *headscratcher*

[Shooty*]

Guys,
was given a Flip Ultra HD video thing for my birthday. Bloody love it. It's fantastic.

So, being reasonable competent, I eschewed the use of the Flip software it comes with. I've shot 37 videos. I've downloaded them by plugging the flip in, and transferring files as if it was just a memory card (rather than through the interface that the software would use).

So far so good.

then I tried to join the clips. I tried Ultravideo joiner, which I've found to be good, even with MP4s. I've NOT tried boilsoft's joiner yet. Before trying that, I wanted to run this past you lot.

The Flip produces MP4 files.

I can only assume that they are VBR, as ultravideo joiner gives an error when it tries to join them, and using the "properties" tab on more than one reveals that they are at different bit rates.

So, I tried the bundled software purely to see if it could join them. And it could.

BUT... and it's a big but... it converts from Mp4, which is a perfectly acceptable format for me, to WMV, and in doing so, manages to double the size of the files! (i.e. 1.2 gb of MP4 video will be turned into 2.4 gb of WMV).

That offends me. It's wasteful of space, and I'd rather join the Mp4s together.

Anyone know any joiners capable to stitching together VBR MP4s, or anyone able to point out where I've gone wrong with some of my assumptions?

Edit: Damn, I'm a muppet. Should try avidemux.

[Shooty*]

Nope, still stuck. Anyone? Anyone? Anyone? Bueller?

[Funkstar]

VirtualDub can do this with AVIs, I wonder if Nandub can do it with mp4s?

the bitrate might bite you again, but worth a shot.

[Shooty*]

*rummages through his 6 or so versions of vdub for nandub*

Thanks, funk.