Allow site administrator to configure preload attribute for files of mimetype audio/mpeg

[kunikla]

Firefox hangs the server's PHP engine when requesting preload of the 7th protected audio file. For sites with Items that have more than 6 protected audio files, and whose themes display all protected files on the Item's page, it will be necessary to set preload="none".

[kunikla]

The problem is that when pre-loading an audio file, the browser keeps the connection open with the server. Each browser places a limit on the number of open connections. The default for Firefox is 6, although the limit is configurable by the user. IE and other browsers set a limit of 2, and configuration is possible, but not simple. Allowing multiple connections to remain open to the server becomes a performance issue when there are many users.

While setting preload="none" keeps the browser from hanging in the browser/platforms tested, since the attribute is only a suggestion for the browser, it cannot be a guaranteed solution across all browsers/platforms.

The solution chosen is to place a restriction on themes used with this plugin. They can only output one <audio> element for a protected file per page. The theme used by the VMA website, BigPicture, has been modified to display a form that allows the user to select which audio file is to be accessed.

The documentation still needs to be updated.