Currently, gnome-music sends multiple PropertiesChanged DBus signals when tracks start and stop playing. I see the following from the org.mpris.MediaPlayer2.Player interface along:

Seven signals on playback start, with the following values:

1. Tracks=[...]
2. ActivePlaylist={...} 
3. Metadata={...}, CanPause=1, CanPlay=1
4. CanGoPrevious=0, CanGoNext=0
5. Metadata={...}, CanPause=0, CanPlay=1
6. PlaybackStatus: Playing
7. Metadata={...}

Three signals on playback stop, with the following values:

1. CanGoNext=0, CanGoPrevious=0
2. CanPlay=0, Metadata={...}
3. Metadata={...}

There's lot of unneeded IPC and wakeups there, also a fair bit of redundancy - especially for the Metadata fields, which are all identical and hence should actually only get reported as having changed once for each track, not up to 5 times.