Qt：No decoder available for type 'video/x-h264 ...；Your GStreamer installation is missing a plug-in.

1. Your GStreamer installation is missing a plug-in.

参考：https://stackoverflow.com/questions/26099139/how-to-fix-gstreamer-error-in-qt5
Ubuntu16.04:
sudo add-apt-repository ppa:mc3man/gstffmpeg-keep
sudo apt-get update
sudo apt-get install gstreamer0.10-ffmpeg
sudo apt-get gstreamer1.0-plugins-bad

Ubuntu 14.04：
sudo add-apt-repository ppa:mc3man/gstffmpeg-keep
sudo apt-get update
sudo apt-get install gstreamer0.10-ffmpeg
sudo apt-get install gstreamer0.10-plugins-ugly
2. No decoder available for type 'video……

参考：MP4 with GStreamer and QMediaPlayer on Ubuntu 16.04 LTS
http://www.open-terrain.org/index.php/Pong/August30th2016QMediaPlayerOnUbuntu16-04LTS