I know that MediaElement.js is part of the WordPress core in WordPress 3.6. I currently use the MediaElement.js plugin on my WordPress 3.5.1 sites. On some pages, we have several players on one page, and we need to specify
preload="none" as a parameter in the MediaElement.js shortcode, because if we don't, some browsers (mainly iOS devices) will try to download all the MP3 files at once.
Here is the shortcode that we currently use:
[audio mp3="filename.mp3" preload="none"]
In WordPress 3.6, with MediaElement.js built-in, will the
preload="none" parameter have any effect in the