Here is my little remuxer: http://code.google.com/p/fuzemux/
This should produce exactly the same container format as SMC does. I have tested it with a few videos and didn’t notice any problems during seeking so far, and running it over a video already converted using SMC seems to produce exactly the bitwise-same file (except for the info tag and the the legacy index which it doesn’t create)
It doesn’t encode the video of course, i.e. the input file already has to be encoded using mencoder or similar with the correct setting. I have written a small Windows batch file that does the complete conversion (calling mencoder first and then fuzemux), or it would have to be integrated in video4fuze as a replacement for AVI-Mux GUI.
