yes i know...
But something strange happened, now i've removed the advancedsettings.xml setting to force amlcodec (like when just updated to 8.90.2) and i've no more shutters.
Maybe was an error, when just updated i've no HW decoder enabled.
I was thinking that <useamcodec>true</useamcodec> had enabled the HW decoder, but now, also without <useamcodec>true</useamcodec> i've the HW decoder on and i can play Jellyfish sample without frame loss or shutter with cpu at nearly 1% .... so a strange things...
But not at 4K