SUMMARY The tool tip over the "Test" button says that it should test the selected device, i.e. the one selected in the scrolling list. However, it appears to ignore the selected device and always plays the test sound to the default one. STEPS TO REPRODUCE 1. Open System Settings - Hardware - Audio and Video - Device Preference 2. Click "Test", the test sound plays through the default (initially selected) device (on my system, "HDA ATI SB, ALC888 Analog Default Device). 3. Select another device (on my system, "HDA NVidia, HDMI 1 HDMI Audio Output") 4. Click "Test" again, the sound again plays through the default device. No sound is heard over HDMI. OBSERVED RESULT Test sound is always played through the default device. EXPECTED RESULT Test sound should be played through the selected device. SOFTWARE/OS VERSIONS Windows: MacOS: Linux/KDE Plasma: 5.14.80 (available in About System) KDE Plasma Version: KDE Frameworks Version: 5.52.0 Qt Version: 5.11.2 ADDITIONAL INFORMATION Phonon backend: VLC Phonon-VLC version (shown on Backend page): 0.10.2 VLC application version: 3.0.3 PulseAudio in use: no Sounds play correctly through HDMI with aplay or the VLC media player. Bug 390270 seems similar, but is referring to the "speaker test" page (the one that is no longer in plasma-desktop as of commit 06c8b9ba on 26 Jul 2018).
I can confirm with phonon-qt5-vlc 0.10.2 on Arch Linux. Test works when onboard sound card (default device) is selected, but it fails when I select hdmi port - I listen test sound via onboard sound card again. Operating System: Arch Linux KDE Plasma Version: 5.15.1 KDE Frameworks Version: 5.55.0 Qt Version: 5.12.1
Have investigated and found a possible solution. See https://phabricator.kde.org/D21015