In iOS you can listen to and control your own iTunes, Pandora, Spotify, Rdio and other music by using iOS's background music feature. Doing this will work in harmony with your video environmental audio, as well as with AirPlay.
iOS
After starting music in another app, you can easily control it from inside of BitGym by using the iOS provided Control Center. To show Control Center over bitgym you need to swipe in from the edge of the screen, but it depends on your iOS device as to which side you swipe from!
On iPhone X (or later) or iPad with iOS 12 or later, swipe down from the upper-right corner of the screen.
On older iPhones or iPads swipe up from the bottom edge of any screen.
Android
First start listening to music in an app outside of BitGym, such as Spotify. Then after switching to BitGym, you should be able to swipe down from the top to reveal the Android status bar. Pull this down and you can play/pause/skip your music.
Warning: Many Android devices have low memory and can crash when trying to use BitGym together with a music player. If you are using a device more than 3 years after its initial launch (example, Galaxy Tab A 10.1" was released in 2016, and is over 3 years old), use with caution over longer workouts as it may result in the app crashing and your workout being interrupted and not saved to your history.
Coached music: Unfortunately the music for coached workouts is baked in with the coaching voice and this is the format in which we have the rights to distribute this content. Hence the music cannot be independently muted. To play your own music you will have to mute the entire coaching - voice and music both.