That's because your operating system, (I guess Windows?) Haves a different sample rate than your Studio One song/project. It would probably be fixed if you set sample rate to 44.2 in Studio One. If so, that means both Windows (VLC/Youtube) als share the same rate and doesn't conflict.
To get it to play everything in 48khz:
In advanced sound settings (both output and input) of Windows, you can setup both input/line and output/audio interface to 48khz. Then you will have sound at all times, when using S1 and Windows apps, if your song settings are 48khz as well.
In general, try preventing having different sample rates between Windows and Studio One.
There is a sound setting in the Studio One I/O set up, where you can automatically close down interface when Studio One is in the background, but it still doesn't really like the switching, I've experienced. (When switching tabs it often happens the sound crashed, needing to replug the audio interface.) So best advice is to have both using the same sample rate, so it doesn't need to switch.
