I found a qt webkit bug
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if on windows 7 computer, and the audio driver had been installed with windows' driver, then use webkit play a html file which contain three or more Audio tag, the it will be hung up.
if the audio driver reinstall with the hardware's driver, it has no the problem.
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Search for your issues here: https://bugreports.qt-project.org/secure/BrowseProjects.jspa
If you are sure, the bug exists ans was not fixes till today, create a new one.