I built QtWebEngine 5.7.1 from git sources to get support of proprietary codecs.
I wrote "WEBENGINE_CONFIG+=use_proprietary_codecs" to the qtwebengine.pro. While qmake was configuring the project, I saw the log saying that MP3 et H264 codecs were enabled.
I spent one day to get QtWebEngine fully compiled with msvc2015 in 32bit and ... The mp3 support still not working !
I use html5test.com to get a quick look of webbrowser capabilities.
I searched a bit and I found out about a ffmpegsumo.dll that wasn't built. I tried to get a 32bits copy over the internet, I don't know really where to put it, I tried different places, that still not working. Finally I thing that's not the good idea.
How QtWebEngine uses mp3 codec ? I'm a bit lost ...