Sorry about the lighting and the (cat) audio issues. Let me know what you think the difference should be between unintelligible and inaudible whispering, or if it even matters to differentiate the two when "inaudible" is generally used as a blanket term. My Patreon: / adequateasmr
To listen while using other apps, switch the player to Picture-in-Picture (PiP) during playback — it keeps playing in a small floating window (the screen stays on).
To listen with the screen fully off, in-browser playback stops by YouTube's design. Open the video in the YouTube app to keep listening where background playback is supported (e.g. with YouTube Premium).
Open in YouTube app