Well, if you want to watch YouTube during your break and you don't want to wait to buffer. I suggest you use aneesoft youtube converter to download YouTube videos on PC and convert them to your devices.
It depends on your music format. If its format is .mp3, you can copy-n-paste to your Galaxy S4. If its format is other formats which Galaxy S4 can't play, you can convert its format with aneesoft video converter and copy-n-paste to your Galaxy S4.