Trying firefox on a fresh install of debian 9.0.0, it plays youtube video fine - sans audio. To figure out whether the silence is due to me having to do something more than hook up the hdmi cable and check that the monitor's speakers are unmuted and set to 50%¹, I thought I'd try www.abc.net.au/news and click on the link to the 24 hr news tv channel. But that evinces an "Error loading player: No playable sources found." OK, I did an apt-get install mplayer, with the same result. Then I added: deb http://mirror.optus.net/deb-multimedia/ stable main to /etc/apt/sources.list, and after that an apt-get update: # apt-get install deb-multimedia-keyring gave "E: Unable to locate package deb-multimedia-keyring" In contrast, this older debian wheezy host plays both sites fine. It would be especially nice to get the audio working, as this new Udoo X86 was bought for its claimed ability to stream to three 4K screens simultaneously. ¹ I also tried an hdmi to vga adaptor, with stereo audio cable plugged into the monitor's audio jack (and the monitor menu-switched to vga mode), but that also gave only silent movies. Erik