I need to calculate the total length of an mp3 file.
Currently I am using a PHP class which I found @ http://www.zedwood.com/article/php-calculate-duration-of-mp3.>
There is actually a library that can run at client-side, attempting to fetch just enough of the MP3 to read the ID3 tags:
http://github.com/aadsm/JavaScript-ID3-Reader
or
Try
HTML File API.
http://lostechies.com/derickbailey/2013/09/23/getting-audio-file-information-with-htmls-file-api-and-audio-element/