Get a file from assets ExoPlayer 2

MainActivity.kt

package com.studio.mattiaferigutti.exoplayertest

import android.annotation.SuppressLint
import android.net.Uri
import android.os.Bundle
import android.util.Log
import android.view.View
import androidx.appcompat.app.AppCompatActivity
import com.google.android.exoplayer2.*
import com.google.android.exoplayer2.source.ProgressiveMediaSource
import com.google.android.exoplayer2.trackselection.DefaultTrackSelector
import com.google.android.exoplayer2.upstream.*
import com.google.android.exoplayer2.upstream.DataSource.Factory
import com.google.android.exoplayer2.util.Util
import kotlinx.android.synthetic.main.activity_main.*


class MainActivity : AppCompatActivity(), Player.EventListener {

    private var player: SimpleExoPlayer? = null
    private var playWhenReady = true
    private var currentWindow = 0
    private var playbackPosition: Long = 0

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
    }

    public override fun onStart() {
        super.onStart()
        if (Util.SDK_INT > 23) {
            initializePlayer("assets:///your_file.your_extension") //"assets:///pillwheel_pills.mp4"
        }
    }

    public override fun onResume() {
        super.onResume()
        hideSystemUi()
        if (Util.SDK_INT <= 23 || player == null) {
            initializePlayer("assets:///your_file.your_extension") //"assets:///pillwheel_pills.mp4"
        }
    }

    public override fun onPause() {
        super.onPause()
        if (Util.SDK_INT <= 23) {
            releasePlayer()
        }
    }

    public override fun onStop() {
        super.onStop()
        if (Util.SDK_INT > 23) {
            releasePlayer()
        }
    }

    private fun initializePlayer(path: String) {
        if (player == null) {
            val trackSelector = DefaultTrackSelector(this)
            trackSelector.setParameters(
                trackSelector.buildUponParameters().setMaxVideoSizeSd())
            player = SimpleExoPlayer.Builder(this)
                .setTrackSelector(trackSelector)
                .build()
        }
        video_view?.player = player
        video_view?.requestFocus()

        val dataSourceFactory = Factory { AssetDataSource(this@MainActivity) }

        val videoSource = ProgressiveMediaSource.Factory(dataSourceFactory)
            .createMediaSource(Uri.parse(path))

        player?.playWhenReady = playWhenReady
        player?.seekTo(currentWindow, playbackPosition)
        player?.addListener(this)
        player?.prepare(videoSource)
    }

    private fun releasePlayer() {
        if (player != null) {
            playbackPosition = player?.currentPosition!!
            currentWindow = player?.currentWindowIndex!!
            playWhenReady = player?.playWhenReady!!
            player?.removeListener(this)
            player?.release()
            player = null
        }
    }

    /**
     * set fullscreen
     */
    @SuppressLint("InlinedApi")
    private fun hideSystemUi() {
        video_view?.systemUiVisibility = (View.SYSTEM_UI_FLAG_LOW_PROFILE
                or View.SYSTEM_UI_FLAG_FULLSCREEN
                or View.SYSTEM_UI_FLAG_LAYOUT_STABLE
                or View.SYSTEM_UI_FLAG_IMMERSIVE_STICKY
                or View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION
                or View.SYSTEM_UI_FLAG_HIDE_NAVIGATION)
    }

    override fun onPlayerError(error: ExoPlaybackException) {
        super.onPlayerError(error)

        //handle the error
    }

    override fun onPlayerStateChanged(playWhenReady: Boolean, playbackState: Int) {
        val stateString: String = when (playbackState) {
            ExoPlayer.STATE_IDLE -> "ExoPlayer.STATE_IDLE      -"
            ExoPlayer.STATE_BUFFERING -> "ExoPlayer.STATE_BUFFERING -"
            ExoPlayer.STATE_READY -> "ExoPlayer.STATE_READY     -"
            ExoPlayer.STATE_ENDED -> "ExoPlayer.STATE_ENDED     -"
            else -> "UNKNOWN_STATE             -"
        }
        Log.d(TAG, "changed state to " + stateString
                + " playWhenReady: " + playWhenReady)
    }

    companion object {
        private val TAG = MainActivity::class.java.name
    }
}

You can find a better example here 🙃