A file with the M4A file extension is an MPEG-4 Audio file. Generally, compared with MP3, M4A is partially designed to replace MP3 (MPEG-3 Audio) as the most popular audio format, with advantages like higher quality, low bitrates and file size.
While Koinonia House did produce M4As which could contain images timed to display with audio ques during playback which provides the functionality of a slideshow, in the mid 2000s when Video download and streaming was prohibitive or expensive, now with the advancement of streaming audio & video, and "Slideshow" M4As becoming unsupported by most players, Koinonia House no longer produces nor supports M4As.