Hi @sixtyseven from Germany 🙂
I’ll respond in the same manner as the questions asked:
a) In the settings for the file field you’ll find “Allowed file types”. Enter mp3 there and you should be good to go!
b) You can get the file wherever you want using get_field(‘filename’). But since your file field is in a repeater you could do:
<?php
$repeater = get_field('repeaterfield');
if( $repeater ): foreach( $repeater as $row ):
//$file contains either a file array, url or ID depending on what you've set in the field settings.
$file = $row['filefield'];
//Now you're free to play around with $file :)
endforeach; endif;
?>
