At first I‘ve installed OggPlay Version 1.6.9 in my mobile, to check whether it is working. It refused to play even though it showed all the particulars of the .mp3 file.
After I switched off and on, it started playing mp3. It played .mp3, .amr (only Narrow Band) and .ogg only; for mp4 or m4a (renamed as .mp4): the counter showed 00:00, but, did not take off. My testing of Version 1.6.9 stopped here.
Then, I uninstalled 1.6.9 and installed 1.7.0. I have to set the defaults in this version again; i.e. open the settings; go to codecs; set the same which are already in the defaults.Wow! It started playing .mp3 .ogg, .amr(Narrow Band) and .aac, but, not mp4 or m4a. I used DBPoweAMP to convert my audio files to convert one format to other format. Files with .aac were produced from .m4a/.mp4 files which are in turn created from .mp3 files using Nero Digital Audio. The default mp4 codec did not respond (still) to the .mp4/.m4a files. In both the versions .amr(Wide Band) did not work.
Hope, I am clear in putting the things up. All the BEST!