There is a service in which a Media Player instance is created to play audio from the server:

class AudioService : Service() {

    private lateinit var mediaPlayer: MediaPlayer

    private val CHANNEL_ID = "AudioService"

    private val audioBinder = AudioBinder()

    fun initialiseAudio(urlFromAPI: String) {

        mediaPlayer = MediaPlayer()

        mediaPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC)
        try {

            mediaPlayer.setDataSource(urlFromAPI)
            mediaPlayer.prepare()
            mediaPlayer.start()

        } catch (e: IOException) {
            e.printStackTrace()
        }
    }

    fun playAudio() {
        if (!mediaPlayer.isPlaying)
            mediaPlayer.start()
    }

    fun pauseAudio() {
        if (mediaPlayer.isPlaying)
            mediaPlayer.pause()
    }

    fun getMP(): MediaPlayer {
        return mediaPlayer
    }

    fun getMPDuration(): Int {
            return mediaPlayer.duration
    }

    fun getMPPosition(): Int {
            return mediaPlayer.currentPosition
    }

    override fun onDestroy() {
        mediaPlayer.reset()
        super.onDestroy()
    }

    override fun onBind(intent: Intent?): IBinder {
        return audioBinder
    }

    inner class AudioBinder : Binder() {
        fun getService(): AudioService {
            return this@AudioService
        }
    }

}

The service connects in the fragment by bindService.

I must create a SeekBar and two TextView with an audio’s position and duration in the fragment.

SeekBar‘s parameters in onViewCreated of the fragment:

binding.skAudioSeekBar.setOnSeekBarChangeListener(object : SeekBar.OnSeekBarChangeListener {
            override fun onProgressChanged(seekBar: SeekBar?, progress: Int, fromUser: Boolean) {
                if (fromUser) audioService!!.getMP().seekTo(progress)
            }

            override fun onStartTrackingTouch(seekBar: SeekBar?) {
            }

            override fun onStopTrackingTouch(seekBar: SeekBar) {
                if (seekBar.progress > 70) {
                    ObjectAnimator.ofInt(seekBar, "progress", 100).setDuration(100).start()
                } else if (seekBar.progress < 30) {
                    ObjectAnimator.ofInt(seekBar, "progress", 0).setDuration(100).start()
                } else {
                    ObjectAnimator.ofInt(seekBar, "progress", 50).setDuration(100).start()
                }
            }

The method for initialization of the SeekBar in the fragment:

    private fun initialiseSeekBar() {
        binding.skAudioSeekBar.max = audioService!!.getMPDuration()
    
        val handler = Handler()
        handler.postDelayed(object : Runnable {
        override fun run() {
            try {

                binding.skAudioSeekBar.progress = audioService!!.getMPPosition()
                handler.postDelayed(this, 1000)

                val durationLength: Int = audioService!!.getMPDuration()
                val durationText: String =
                    DateUtils.formatElapsedTime((durationLength / 1000).toLong())
                binding.tvAudioDuration.text = durationText

                val positionLength: Int = audioService!!.getMPPosition()
                val positionText: String =
                    DateUtils.formatElapsedTime((positionLength / 1000).toLong())
                binding.tvAudioPosition.text = positionText

            } catch (e: Exception) {
                binding.skAudioSeekBar.progress = 0
            }
        }

    }, 0)
}

The problem is that the app crashes when the service starts (FATAL EXCEPTION: main java.lang.NullPointerException). LogCat points to the first line of the initialiseSeekBar(). If this method is not used, the service starts normally.