Hi there!
Got my RPi4 on tuesday and tried if I can already replace my Pi3 with it. Running the current LibreElec 9.1 Alpha With Kodi 18.3 on it. So far everything seems fine but I encountered some problems especially when using the internal frame grabber to be used with selfmade Hyperion Ambilight.
As soon as Hyperion is installed and running, grabbing the actual frames to display the edge colors to the LEDs behind my TV, the system gets very laggy, CPU temperature increases up to 70-72°C until it sometimes crashes and reboots. Also when having Hyperion running, the OSD when playing a 4K (HEVC) video is not working anymore. Pausing a movie (permanent OSD overlay) would result in a black screen on the TV. Sometimes with flickering (in that case you are able to see the frozen video + OSD for a second) (the OSD seems very big then, like zoomed in with 300%) and very stuttering performance. Sometimes it also looses the audio playback, when continuing again.
When the 4K (HEVC) video is playing and the OSD is not triggered/overlayed, the Framegrabber gets crazy. Everything is flickering, even if some correct colors are applied to the LEDs. Looks like 50% of the driven LEDs get the wrong signal and displaying various colors. Jumping colors. Everythings blinking/flickering.
Btw: Even if playing a 1080p video (which is possible without playback or OSD issues), the Framegrabber seems to have some but less problems. Also stuttering LEDs but I would say around 5% are wrong.
I've actually also had a fresh install with the same settings as above when the 4K video can't even be played, but always was shown for a second, then black screen for 5, showing for 1 second... and so on. (The fresh install was to test if anything on my end may be the problem)
Once the Hyperion daemon is stopped, (also removed the spi-on flag from the config.txt) everything works like a charm again. Except Ambilight 
Besides the one thing with the temperature mentioned first. It seems to get very hot when the Framegrabber is active.
It looks like the system gets very unstable and missing some kind of vsync (thats how it looks), when the CPU temperature is around 70°C or above. Rebooting won't kill the issue so it must be related to heat/temperature. Shutting down, having the CPU cooled down a bit, restarting and everything is fine again.
Maybe you guys are able to fix that. Or possibly there is already a fix available?!
Thank you very much! Keep up the great work. Always loved my LE with Ambilight and with the power of a RPi4 it gets even better, because no other device is necessary to display 4K videos AND having a working Ambilight (hopefully soon ;D)
Hyperion can be installed with this script:
curl -L --output install_hyperion.sh --get https://raw.githubusercontent.com/tvdzwan/hyperion/master/bin/install_hyperion.sh
sh ./install_hyperion.shYou probably need a valid config to use it. Just use mine. Shouldnt matter whats inside, because you have no LEDs at all. Just be sure Hyperion is started, the SPI is activated and the frame grabber is used that way. (Remove the ending .txt from the file; was needed for uploading). The config goes into: \\<ip>\Configfiles
hyperion.config.json.txt
