What problems do you have with backends?
I couldn't get working audio when PulseAudio (somehow it was default) was compiled in without Alsa/SNDIO etc...
So I've decided to check what is working and in the middle I found that event sounds are not installed "BIG LOL". So finally I can't say that PulseAudio doesn't work and I'm not going to recompile whole projects which took 5 hours. ZFS+Snaphost before KDE5 has been installed. However, missing audio event sounds are not part of
x11-themes/plasma5-breeze but Ogg event audio files are included in
x11-themes/plasma5-oxygen. So I waste a lot of time on compilation. When I got it working I immediately abandon Alsa and stupid PulseAudio. FInally I am happy with SNDIO, and my surprise was that Konqueror on
html5test.com shows me that there is audio support while Youtube won't play any audio to output device, for that I found that I have missing port
audio/alsa-sndio + remember to add default SNDIO settings mentioned in port message. I've test both web engine KHtml and WebKit, in both cases sound is working as expected. I'm using VLC backend without gstreamer which didn't work for me also.
Konqueror: Interesting is that, without
audio/alsa-sndio I am capable to play audio with html5, but youtube audio doesn't play, it seems that for youtube webengine is using alsa while for html5 audio the output is redirected to phonon backend ? That's only assumption and I may be wrong with that.
In the meantime I was thought that AlsaLib can be easily excluded from dependency list for
www/qt5-webengine, I have a small patches but nothing works. I was thought that linking with SNDIO instead of AlsaLib is the right choice, but even if I change any words "-lasound" (in the whole sources +++ makefiles/cmake/ninja +++ /usr/local/libdata/*) args to "-lsndio" linker will always prefer alsa somehow. I didn't investigate that stupidity but ok, I got what I expect.