Make mp4/h264 video work in QtWebEngine on Windows

When I point the QtWebEngine instance at a html5 test page (http://www.quirksmode.org/html5/tests/video.html) I see the WebM video, the Theora video, but not H.264/MP4.

Enabling mp4/mpeg4/avc support for Qt5 WebEngine on Linux said to build qtwebengine from source, so I'm building everything.

I downloaded this source package: http://download.qt.io/official_releases/qt/5.5/5.5.0/single/qt-everywhere-opensource-src-5.5.0.zip

I followed the directions for other dependencies, and then tried building with these commands:

configure -prefix %QT_ROOT%\build -opengl dynamic -release -nomake examples -opensource -confirm-license  -qt-libpng -qt-libjpeg -openssl -qt-pcre -no-cups -no-dbus -skip qtwebkit -skip qtconnectivity -skip qtdoc -skip qtgraphicaleffects -skip qtsensors -skip qtserialport -skip qtwebkit-examples -skip qtquick1 -skip qt3d -skip qtwebengine
nmake
nmake install
cd qtwebengine
..\build\bin\qmake WEBENGINE_CONFIG+=use_proprietary_codecs qtwebengine.pro
nmake
nmake install

Then when I build the web browser example against my new build, I get the same results as before. When I try to look for evidence that it did or didn't build the codecs, I see that ffmpegsumo.dll was created. I see no errors in the javascript console about this. I've tested with other test web pages beyond quicksmode and no results there either.

My solution was to upgrade to Qt 5.6.1. Otherwise, I followed the directions in the original question and this time got a working result. Most notable, the qmake WEBENGINE_CONFIG+=use_proprietary_codecs did confirm it was checking and configuring h264 and mp3.