Your audioElement tag should contain three source formats. The first is OGG audioElement which is an open standard, supported by Firefox and Chrome. The second is our old friend MPEG-1 layer 3 (MP3) which is a commercial proprietary format supported by Safari. The third is a plain old WAVE file, which is what Opera wants to hear. Browsers will attempt to use sources in markup order, so for example Safari would fail to read the OGG format source, and use the MP3 source instead, while Opera will fail on the first two sources and use the third WAVE source.