A customer requested a feature for a social audio rooms app on Android, which involved transforming certain rooms into "radio stations" by allowing hosts to stream local music while speaking. Since WebRTC on mobile doesn't support adding custom audio tracks, significant modifications were made to the WebRTC source and Android SDK to enable mixing audio captured from the device's microphone with local audio. The process involved capturing microphone audio using WebRTC's JavaAudioDeviceModule and capturing local device audio with Android’s AudioRecord class, which required Android 10 or above. A callback mechanism was employed to synchronize the capture of audio bytes from both sources, which were then mixed programmatically to create a combined audio stream broadcasted to listeners. This solution also provides the flexibility to replace microphone audio with local audio if needed. The changes aim to enhance the app's functionality, and developers are encouraged to share feedback on the implementation through Discord.