In the past, the integration of music into video and stories snapchat has always been difficult as users could not (and cannot) upload pre-recorded videos or use third party applications .
Luckily, Snapchat users got the message that users want music in their snaps, so an update to the app ended up allowing music to play on your device in the background while recording video messages.

How to send SnapChats with music
The addition of a music feature to Snapchat is what speeds it up with other competing social media apps, especially Instagram .
It’s also pretty easy to do and you don’t have to do any complicated extra steps on the Snapchat app to add music to your videos.
Prior to this update, if you wanted music to play in a video on Snapchat, you needed another device or computer to play it. Users also took advantage of the third-party music app Mindie before Snapchat disabled its access.