On this site
http://www.spiegel.de/kultur/musik/keith-jarrett-neues-album-last-dance-im-vorab-stream-a-973857.html
there is a frame containing a music stream. When I loaded that site the matrix only showed me to whitelist the frame cell for player.muzu.tv. After that I had to reload the site several times and had to whitelist the plugin cells for damoh.muzu.tv, player.muzu.tv, media3.muzu.tv and static.muzu.tv and the script cell for files.muzu.tv. (I didn't whitelist the complete muzu.tv domain.)

The interesting thing is that I also have to whitelist the script cell for player.muzu.tv although this cell is empty. It doesn't contain any number. Once I blacklist that empty cell again, the stream stops to play.