On my phone at least there is an audible gap if you close the phone with the app playing, which doesn't happen with anything else. My guess is that it's fiddling with something in the background to only fetch audio instead of video.
sure
I always assumed this was because they are switching from builtin app code to their override for the feature... I tried opening a video and locking immediately and it seems like it saturates the download speed until the video is buffered X seconds to the future. Another piece of evidence against it is that when unlocking, it immmediately shows the video: it would need to buffer if only the audio was loaded
You have a point on this
> when unlocking, it immmediately shows the video
On my phone, on mobile data at least, it takes ~5 seconds to display the video again.
5 seconds is a lot of time. This shows that it has to load the video
It is immediate on all phones I have tried it on. 5 seconds is unbearable.
I assume YouTube Vanced does the same as NewPipe which only fetches the audio in background mode
Right. "NewPipe does not use the official YouTube API, but instead scrapes the website for video and meta-data such as likes, dislikes, and views.". So it can do it. If they used the YouTube API this would not permitted.