diff video vs audio: https://arxiv.org/ftp/arxiv/papers/1101/1101.0608.pdf
video lag: https://alantechreview.blogspot.com/2020/05/a-5-tv-input-lag-tester-using-raspberry.html
to run without root, adduser user gpio and sudo sh -c 'echo none > /sys/class/leds/led0/trigger'
more expensive: https://www.leobodnar.com/shop/?main_page=product_info&products_id=212