Hello
Yes, I can't render in x264 nor Xvid. I have installed Kdenlive from PPA
https://launchpad.net/~sunab/+archive/kdenlive-release
and have all extras installed. Still, no luck. I will provide all kind of outputs - just tell me what you need to investigate.
try running the config wizard from Kdenlive settings menu, and follow all steps. This dialog does the codec detection... If you still cannot encode to h264, in a terminal:
ffmpeg -formats
and copy paste result
Hmm, then you probably have several installations of MLT or FFmpeg...
Try deleting the Kdenlive config file in $HOME/.kde/share/config/kdenliverc
And restart Kdenlive.
If that doesn't help, check that you don't have another install of MLT of FFmpeg in /usr/local
Ok, sorry I checked on my system and here is the situation:
ffmpeg -formats
lists h264 as available video codec
However, for me in melt, h264 encoding is listed as libx264, which should appear in the config wizard list. It is at the bottom of the list, see picture:

If you don't have that libx264 entry, can you paste the result of:
melt noise: -consumer avformat: vcodec=list
If you have libx264 in the config Wizard, can you copy / paste the encoding params from the render widget (click on the blue (i) icon to see the params when you select h264).
Wizard did not help. But anyway - pic:
http://img7.imagebanana.com/img/1us5b021/Zaznaczenie_014.jpeg
output:
http://pastebin.com/raw.php?i=pFn7s1Jc