I tried .MP3 and "downloaded" music from GMusic. Is there a way to link "My library" to a specific folder?
Google Music stores offline mp3 files in /sdcard/Android/data/com.google.android.music/cache/music. The files are named as integers without tags, so you are best off making copies, renaming and tagging (if you wish), and putting them on the external sd or another internal folder, e.g. /sdcard/My Music.
There is no way to scan specific folders in the stock HTC Music UI AFAIK. Easiest way to get it to detect files that don't show in the player's library is to make sure they are in a folder in /sdcard/ or the external sd, and reboot; should rescan for files and pick them up them. Perhaps someone else knows how to tweak the library, with an app or editing a file?
Frankly, I have broken my stock player at the moment from flashing ROMs and not wiping properly (ran out of Charmin Ultra lol
) Else I'd troubleshoot the problem more.
Either way, I find the HTC Music app lacking compared to PowerAmp (scans everything lightning fast), doubletwist (good for iTunes integration) and other offerings on the Play Store. I have simply done the Beats Audio mod to all sound output:
http://xdaforums.com/showthread.php?t=1587168 Then use whichever music player I want.