I've come to the conclusion that the RPi4 (running LibreELEC-RPi4.aarch64-12.0-nightly-20230520) will not do what I want - record 2 programmes using my Hauppage tuner whist watching a movie. I've tried several approaches (eg record to SD card, record to USB HDD, force_turbo=1) and I get varied effects (eg audio lost, freezing, video speed up, loss of sync between audio & video) so I've decided I need to buy a more powerful machine.
I've found the Intel page which tells me which NUCs support CEC but I can't find anything which tells me about other machines. Since other machines are generally at a lower price point than Intel I'd like to be able to consider them. Does anyone know a resource which I can use to see if a machine supports CEC before I buy it?