iTunes won't play music or podcasts

iTunes 12.8.0.150 on Windows 10 64-bit. iTunes displays and browses the music and podcasts fine, but when I double-click anything, it shows the pause button as if it were playing but the progress bar does not move. In the library display, the little blue dot of the selection being "played" is replaced by a speaker icon.

I closed and reopened iTunes to no avail. I'm going to try rebooting the system next.