I'm using Debian Testing and yesterday I had a substantial (safe) upgrade of packages. One of the effects of the upgrade seems to be that VLC (and KDE's Dragon player) no longer can use the H264 video codec. This change does NOT effect Kaffeine or any mplayer based media player (Kmplayer and Gnome-mplayer work fine).
I have some videos encoded as H264 in MKV containers. When skipping too much in VLC or Media Player Classic the media players will either crash outright or the whole system will lock up, on occasion a blue screen but most of the time it'll sit there (and no, I've tried CTRL+ALT+DEL).