upnp show music genres and artists

[ari@…]

The code is already in place, but commented out. I can't see why, since it appears perfectly correct and others report that recompiling with this code enabled works perfectly.

​https://github.com/MythTV/mythtv/blob/master/mythtv/programs/mythbackend/upnpcdsmusic.cpp

All we need to do there is remove the commented out artist and genre groupings. This would dramatically improve upnp usefulness.

In addition, a related patch to enhance the sort order for recordings might be considered: ​https://github.com/MythTV/mythtv/pull/19