Hi - I have no idea, a customer sent them to us. m4a is a great idea because no matter how many times we told people in the past to send us an mp3 or wav, invariably they sent us m4a files saying "sort it out, dunno how to convert, that's not my job" so I was happy that this was now available. The file are recognised by other apps as m4a though so the encoding appears to be correct. I will try and create a few myself and see if I encounter the same issue.