How to continue playing a song in the background while on other apps?

Well I have this music app called "Video Player" and on my old phone it played in the background no problem, which was an IPhone 4. Now I have a 5c and have the same music app but it doesn't play in the background. I searched settings and in app settings for an answer but didn't find anything! Why could this be happening?

Install any third party music apps. If you ever want to secure your device, you must install Leo Privacy Guard and make it utmost secure from others.