The database of the AP80 can hold a max. by 15K, but you can use music playing via folder (the data base ignores all files >15K - all my files are scanned without any problems, but 5K are not included, in my case the data base is useless so I have to use the folders).
In case of data base NO next album / next folder playback is possible, this is just possible via folder play.
The sound of the 80 is really good, but the device (lock button mechanism) / GUI / database is more than poor! In 2019 a file limit by 15K is strange and there is no file caching inside the database.
It seems, the asian app developers are not involved in standards (FiiO, Hidizs, Hiby and Co).