FFmpeg plugin for QMediaPlayer in QtMultiMedia

In QtMultiMedia sub module, there are wasm and ffmpeg plugins for QMediaPlayer.

The wasm plugin seems not to support 10 bits and HDR videos and some videos playing to show incorrectly, seems due to data format issues.

I enable ffmpeg plugin in wasm environment and it worked but with bugs.

1. Sometimes, playing stucked and UI has no response anymore
2. sometimes it shows “blocking on main thread is very dangerous ”
3. it can play and decode 10bits video and many format
4. Also show correct video compared to the wasm plugin 

WASM emscripten 3.1.50 , chrome browser
The example I used is 
https://github.com/qt/qtmultimedia/tree/dev/examples/multimedia/player