Are .MP3 files with capital letter extensions allowed in [audio] shortcode?
No, apparently not. Until this behavior is changed in version 3.7 you can add this filter to your theme’s functions.php file to include additional extensions. Edited: I’ve updated the filter with better code suggested in the comments. Lower case and uppercase extensions function my_custom_audio_extensions( $exts ) { //merge array of upper case extensions with default … Read more