Initially, we thought about manipulating audio samples and removing some of them in order to trim or mix songs. But this turned out to be problematic because we would have to download each song separately in order to analyze them, so we decided to depend on song playback. This solved issues like battery draining and higher bandwidth usage. For crossfade, we use two players and synchronize them together based on the playback. For each sound effect, we use a separate player that starts playing based on main song playback. A similar approach was taken for other features like tempo change.

We integrated multiple players within the app such as Chromecast, AppleMusic, and Airplay. It required us to create a robust abstraction over all those players to seamlessly switch between all media sources.

To make the app work offline we had to introduce both API responses and media data caching mechanisms.