Can't get multiple audio layers on a page to play.

Question

One of my clients has an online course in which each weekly lesson is presented on one web page. A typical lesson includes three MP3 audio files for playback only (no download). The site is built in WordPress, and is using the MediaElement.js HTML5 audio player plug-in, which produces HTML5 code with a fall back to Flash. This system has worked properly for almost two years. A student complained yesterday that she could only get the first audio to play on the Week 1 page; the other two just did nothing when she clicked their Play buttons. I was able to confirm that such was the case in FireFox 34.0 and IE 11, but Chrome and Safari are still working fine. Just focusing on FireFox right now, I have tried several other player plug-ins, with no luck, and even hand crafted HTML5 audio tags in place of the player shortcodes, but got the same result. WordPress and the players are all latest versions. I have also made sure that my FireFox QuickTime and Flash plug-ins are latest versions, but still no change. The console shows a message that the audio file could not be decoded whenever the non-playing players are clicked. Also, in trying different course pages, I find that sometimes the successful player is the first one on the page, but not always; the second or even the third player is sometimes the successful player, while the other two will not play.
I would appreciate any information that could help me get this working again. Now I will go talk to Microsoft about version of this problem. :)

Answer 1

I've called the big guys to help you. Good luck.
Some added toolbar and anti-virus add-ons are known to cause
Firefox issues. '''Disable All of them.'''
Many site issues can be caused by corrupt cookies or cache.
* Clear the Cache and
* Remove Cookies<br> '''''Warning ! ! '' This will log you out of sites you're logged in to.'''
Type '''about:preferences'''<Enter> in the address bar.
* '''Cookies;''' Select '''Privacy.''' Under '''History,''' select Firefox will '''Use Custom Settings.''' Press the button on the right side called '''Show Cookies.''' Use the search bar to look for the site. Note; There may be more than one entry. Remove '''All''' of them.
* '''Cache;''' Select '''Advanced > Network.''' Across from '''Cached Web Content,''' Press '''Clear Now.'''
If there is still a problem,
'''[https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode Start Firefox in Safe Mode]''' {web link}
While you are in safe mode;
Type '''about:preferences#advanced'''<Enter> in the address bar.
Under '''Advanced,''' Select '''General.'''
Look for and turn off '''Use Hardware Acceleration'''.
Poke around safe web sites. Are there any problems?
Then restart.