I using kdenlive 0.9.4 in ubuntu 12.10, and have run into some problems when rendering to h.264-format. Mpeg2 works nicely, as do mp4, but often (but not always!) when I render to h.264, the file contains only sound, no video. I make sure the "export audio" is grey-ish ("automatic"), and have also tried with it blank or with a clear mark - without success. However, it seems that *sometimes* it works, maybe when the computer is newly rebooted - I have not been able to be sure about this, as the successes are difficult to produce...
Any ideas on what might be wrong?