kalkov, thank you for that clear explanation.
Given the video problems you reported yesterday that exist in 5.3, then I should be pleased that I did not manage the upgrade. I shall wait for 5.4 and then install on a separate SD.
The improvement in playing video in 5.2 is much appreciated. It is now watchable, audio is good. At standard def the video can be slightly jumpy - not quite smooth enough when e.g. watching an orchestra playing at speed. The effect is amusing - looks like the players have been replaced by very advanced androids.