Note most (all?) video players introduce quite some playback latency by default due to buffering - which is _really_ annoying using them as a 'monitor'. You'll

Note most (all?) video players introduce quite some playback latency by default due to buffering - which is _really_ annoying using them as a 'monitor'. You'll want to look up the flags/settings for low latency playback to make it more usable, e.g. for mpv: https://mpv.io/manual/stable/#low-latency-playback https://mpv.io/manual/stable/#low-latency-playback