How to play .mp4 in ExoPlayer?

ExoPlayerMp4.kt

package com.halil.ozel.exoplayerdashsample

import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import com.google.android.exoplayer2.ExoPlayer
import com.google.android.exoplayer2.MediaItem
import com.google.android.exoplayer2.source.MediaSource
import com.google.android.exoplayer2.source.ProgressiveMediaSource
import com.google.android.exoplayer2.upstream.DefaultHttpDataSource
import com.halil.ozel.exoplayerdashsample.databinding.ActivityMainBinding


class MainActivity : AppCompatActivity() {
    private lateinit var binding: ActivityMainBinding
    private var exoPlayer: ExoPlayer? = null
    private var playbackPosition = 0L
    private var playWhenReady = true

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityMainBinding.inflate(layoutInflater)
        val view = binding.root
        setContentView(view)
        preparePlayer()
    }

    private fun preparePlayer() {
        exoPlayer = ExoPlayer.Builder(this).build()
        exoPlayer?.let { exo ->
            exo.playWhenReady = true
            binding.playerView.player = exo
            exo.setMediaSource(setMediaType())
            exo.seekTo(playbackPosition)
            exo.playWhenReady = playWhenReady
            exo.prepare()
        }
    }

    private fun releasePlayer() {
        exoPlayer?.let { player ->
            playbackPosition = player.currentPosition
            playWhenReady = player.playWhenReady
            player.release()
            exoPlayer = null
        }
    }

    private fun setMediaType(): MediaSource {
        val defaultHttpDataSourceFactory = DefaultHttpDataSource.Factory()
        val mediaItem = MediaItem.fromUri(URL)
        return ProgressiveMediaSource.Factory(defaultHttpDataSourceFactory)
            .createMediaSource(mediaItem)
    }

    override fun onStop() {
        super.onStop()
        releasePlayer()
    }

    override fun onPause() {
        super.onPause()
        releasePlayer()
    }

    override fun onDestroy() {
        super.onDestroy()
        releasePlayer()
    }

    companion object {
        const val URL =
            "https://storage.googleapis.com/gtv-videos-bucket/sample/BigBuckBunny.mp4"
    }

}