Whilst we use standard MP4 video containers for all videos that are streamed on our platform, some Linux systems require these codecs to be manually installed due to licensing.
On some Linux based systems, especially CentOS, 'GStreamer' needs to be installed in order to decode and watch the videos. Other websites (YouTube for instance) will automatically fall back to a different codec, such as Adobe Flash, which is why they may work, when videos on A Cloud Guru do not.
In order to fix this, ensure that GStreamer is installed for your operating system:
The last line in particular for installed GStreamer via Yum.
This link has some more in depth information around how the versions of GStreamer that ship with CentOS are too old for most videos and need to be updated: https://media.librelamp.com/gst.