Configure volume level for left and right channels in a stereo audio in Swift
This is more as a reference project of an implementation of dynamic volume level changing for stereo audio player, but it's fully working player that can be used right away.
AVPlayer and MTAudioProcessingTap are used under the hood.
Mono mode is made via two AVPlayers to play original left and right channel in both channels. It should be possible to make in process( function of AudioTap.m file by manipulating audio buffers and have just one AVPlayer, but I couldn't do it so made a simple solution with two players.
Try out the Demo project
let url = Bundle.main.url(forResource: "stereo-test", withExtension: "mp3")!
let player = StereoAudioPlayer(contentsOf: url)
player.play()
player.leftLevel = 0.5
player.rightLevel = 1
StackOverflow
https://stackoverflow.com/a/37763490/1236681
Processing AVPlayer’s audio with MTAudioProcessingTap
https://chritto.wordpress.com/2013/01/07/processing-avplayers-audio-with-mtaudioprocessingtap/