I watch Channel4 a lot and I don't have any issues with it using xineliboutput or my Reel HDe (read: it's not noticable). But if you could tell mee the German channels, I could check with those as well.
For me the frontend doesn't seem to make a difference: - vdr-xine/xine-ui - vdr-xine/gxine - xineliboutput show the same behaviour.
Can I ask which xine-lib version is behind your xineliboutput?