Cyanogenmod not saving video + root missing
The problem was that the back video camera was set to record in 4K resolution.

The fix for the video camera issue is:


Go to the default camera app.
Swipe from the left to see the "Camera" "Video" Menu, on the bottom right corner the is a gear icon, press it to go to camera settings.
Go to resolution and quality and change the back camera video quality to 1080p instead of 4K.


For the root problem I found that you need to enable root once you have Cyanogenmod so you need to:


  Activate Developer options (settings->about phone, tap 'Build number' multiple >times).
  In Developer options, tap 'Root access' and enable either "Apps" or "Apps and >ADB"


http://wiki.cyanogenmod.org/w/User:PsychoI3oy#Superuser_on_CyanogenMod_12.0