Try using the same code, using absolute instead of relative paths:
<video height="270" width="480"
src="http://cdn.kaltura.org/apis/html5lib/kplayer-examples/media/bbb_trailer_iphone.m4v"
poster="http://cdn.kaltura.org/apis/html5lib/kplayer-examples/media/bbb480.jpg"
durationHint="00:04:44">
</video>
If this does not work, their CDNs can block external referrers, so try saving the files to your own local server and use absolute paths for them.
NOTE. You do not need to use absolute paths, but it definitely helps with troubleshooting.
, , , JavaScript ; iOS 5 +.
iOS 3 :
http://videojs.com/2010/09/ipad-iphone-video-poster-fix-bonus-javascript-placement-fix/