html5 audio used to work for me a while ago, audio and video where both shown as supported by test sites just that video was missing codecs. By now, audio and video tags are unsupported. This is not an upstream bug, video and audio works in other distributions such as Ubuntu. I'm currently using media-libs/phonon-4.5.0[vlc] media-libs/phonon-vlc-0.3.2 kde-base/phonon-kde-4.6.2 x11-libs/qt-webkit-4.7.2 Other versions and combinations (such as phonon xine) have the same issue. I don't really know which part is to blame here. I tried google and the forum without success, although I don't seem to be the only one having this problem. Reproducible: Always
Probably media-libs/phonon isn't detected by qt-webkit, which expects x11-libs/qt-phonon to be installed instead.
qt-webkit now requires either gstreamer or the multimedia module from qt-mobility to enable HTML5 audio/video support. See src/3rdparty/webkit/Source/WebCore/features.pri
Fixed in qt-webkit-4.8.0-r1, which will be unmasked when all reverse deps are fixed (bug #404493).
kde 4.8.1 just hit the tree. Please unmask qt-webkit and qt-qt3support.