WordPress.org

Supported file formats?

Just mp3 files.

Theme requirements?

Themes need the wp_head() and wp_footer() calls in them.

Mp3 encoding?

Mp3's should be constant bit-rate (CBR) encoded at sample rates 44.1kHz, 22.05 kHz, 11.025 kHz, though variable bit-rate (VBR) files seem to work ok.

Player says connecting but never plays?

Check the filename spelling and the path/uri are correct. Remove any accented letters from mp3 filenames (and re-upload if they're from the library). Check the mp3 encoding (see above).

Header and footer players?

Use widget areas (if available), or use the mp3j_addscripts() and mp3j_put() functions in template files. See help in the plugin for an example.

Player appears but something is broken?

Any number of reasons but the most commonly seen problem is poor use of a CDN or jQuery in theme files, check the page source for repeated scripts (including jquery-ui).

Report bugs/issues?

Either on the forum at WordPress, or here.