MacBook Pro 2015 Speaker Trouble

Hi.

It just occured to me that sound on speakers on my Mac Pro (Retina, 13-inch, Early 2015) reduced to half or even less of the original level. I did check everything in System Preferences and the volume bar is set to full with the mute button unticked. I also realized that while watching videos on the internet (youtube or other internet source) the volume is almost muted (I did put the volume bar in the video to the max) but in Apple Music is just reduced by half. I would be really happy if anyone could help me figure out what the problem is.

Thank you very much!

Jure