From LQWiki

HelixPlayer and RealPlayer

• When installing HelixPlayer on Fedora, make sure you are using the official RPM distributed by the Fedora Project. (HelixPlayer-1.0.6-1.fc4.2 as of 2 December 2005.) The RPMs distributed on the HelixPlayer community site don't necessarily put the MIME-related files in the right places. This could cause your web browser to be confused about how to handle streaming audio.

• To get RealPlayer-10.0.6.776-20050915 working properly, I had to first uninstall the unofficial (non-Fedora-distributed) HelixPlayer RPM, then install HelixPlayer-1.0.6-1.fc4.2 before installing the RealPlayer. You might want to try this if your web browser isn't handling RealAudio content properly, especially in .smil files (as on npr.org, for example).