Hi Frank,
stream.flac that is shown is no file. It is a flac stream via DLNA from my laptop to RuneAudio. (sorry for not making that clear in my previous post)
To do so, I use "pulseaudio-dlna -c flac" (see https://github.com/masmu/pulseaudio-dlna) on my Ubuntu laptop to stream audio to any network UPnP renderer (in this case RuneAudio).
Using a Android device with any UPnP app (i.e:BubbleUPnP) allowing streaming audio from the phone to RuneAudio should create very similar scenario.
I tried streaming in other format (MP3, WAV) but same issue.
As Pete mentionned, CPU usage only happens when browser tab is being displayed (it doesn't have to be in-focus though... in my screenshots, the Terminal is in focus)
Thanks!