What kind of source material support embedded QtWebKit browser has? Does it support MPEG-4, WebM or Theora and is this support available through compilation?
I was mostly looking desktop platforms (Linux)
QtWebKit is not video player, but it supports extensions like adobe flash, so if you embed some kind of flash player in html you displaying, it will play all videos which can be played in your OS with flash. Another approach is to use Phonon module, which connects to your video codec system and could play all formats which have codecs installed for them.
Also, html5 support will be added in qt webkit version 2.2, which is still in alpha.