I am looking to implement Google\'s ExoPlayer in my app. Their documentation seems pretty vague to me, and all I am looking for is to play a video from an URL, no c         
        
Here is a new Github Library named MagicalExoPlayer, That based on ExoPlayer.
Supports MP4, HLS and Dash.
Supports custom Aspect Ratios
Support FullScreen
A VideoView would be a better idea in case you wish to display only a Video URL. ExoPlayer requires some developmental effort, even for invoking its simple instance. However, there is an advantage of faster and more efficient playback, backed up by an active open-source community. This link provides a good walk through the implementation giving ample reasons to switch to ExoPlayer. Ofcourse, do checkout the official developer guide, the updated version has split modules for simpler implementation.
//Add dependency in manifest file 
    implementation 'com.google.android.exoplayer:exoplayer:2.7.3'
// Add exoplayer in your layout(xml) file 
 <RelativeLayout
        android:id="@+id/rl_video"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
    <com.google.android.exoplayer2.ui.PlayerView
        android:id="@+id/videoFullScreenPlayer"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="#A6000000"
        app:controller_layout_id="@layout/exo_playback_control_view"
        app:player_layout_id="@layout/exo_simple_player_view"
        app:repeat_toggle_modes="none"
        app:show_timeout="45000"
        app:surface_type="texture_view"
        />
        <ProgressBar
            android:id="@+id/spinnerVideoDetails"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_centerInParent="true"
            android:layout_marginStart="8dp"
            android:layout_marginTop="8dp"
            android:layout_marginEnd="8dp"
            android:layout_marginBottom="8dp"
            android:indeterminate="true"/>
    </RelativeLayout>
// open video with below code
// initialise varible 
 PlayerView videoFullScreenPlayer;
    SimpleExoPlayer player;
    ProgressBar spinnerVideoDetails;
// find Id 
 videoFullScreenPlayer = findViewById(R.id.videoFullScreenPlayer);
        spinnerVideoDetails = findViewById(R.id.spinnerVideoDetails);
// open video method 
private void setUp() {
        initializePlayer();
        if (videoUrl == null) {
            return;
        }
        buildMediaSource(Uri.parse(videoUrl ));
    }
    private void initializePlayer() {
        if (player == null) {
            BandwidthMeter bandwidthMeter = new DefaultBandwidthMeter();
            TrackSelection.Factory videoTrackSelectionFactory = new AdaptiveTrackSelection.Factory(bandwidthMeter);
            TrackSelector trackSelector = new DefaultTrackSelector(videoTrackSelectionFactory);
            // 1. Create a default TrackSelector
            DefaultLoadControl loadControl = new DefaultLoadControl.Builder().setBufferDurationsMs(32*1024, 64*1024, 1024, 1024).createDefaultLoadControl();
            // 2. Create the player
            player = ExoPlayerFactory.newSimpleInstance(this, trackSelector, loadControl);
            videoFullScreenPlayer.setPlayer(player);
        }
    }
    private void buildMediaSource(Uri mUri) {
        // Measures bandwidth during playback. Can be null if not required.
        DefaultBandwidthMeter bandwidthMeter = new DefaultBandwidthMeter();
        // Produces DataSource instances through which media data is loaded.
        DataSource.Factory dataSourceFactory = new DefaultDataSourceFactory(this,
                Util.getUserAgent(this, getString(R.string.app_name)), bandwidthMeter);
        // This is the MediaSource representing the media to be played.
        MediaSource videoSource = new ExtractorMediaSource.Factory(dataSourceFactory).createMediaSource(mUri);
        // Prepare the player with the source.
        player.prepare(videoSource);
        player.setPlayWhenReady(true);
        player.addListener(this);
    }
    private void releasePlayer() {
        if (player != null) {
            player.release();
            player = null;
        }
    }
    private void pausePlayer() {
        if (player != null) {
            player.setPlayWhenReady(false);
            player.getPlaybackState();
        }
    }
    private void resumePlayer() {
        if (player != null) {
            player.setPlayWhenReady(true);
            player.getPlaybackState();
        }
    }
    @Override
    protected void onPause() {
        super.onPause();
        pausePlayer();
       /* if (mRunnable != null) {
            mHandler.removeCallbacks(mRunnable);
        }*/
    }
    @Override
    protected void onRestart() {
        super.onRestart();
        resumePlayer();
    }
    @Override
    protected void onDestroy() {
        super.onDestroy();
        releasePlayer();
    }
    @Override
    public void onTimelineChanged(Timeline timeline, Object manifest, int reason) {
    }
    @Override
    public void onTracksChanged(TrackGroupArray trackGroups, TrackSelectionArray trackSelections) {
    }
    @Override
    public void onLoadingChanged(boolean isLoading) {
    }
    @Override
    public void onPlayerStateChanged(boolean playWhenReady, int playbackState) {
        switch (playbackState) {
            case Player.STATE_BUFFERING:
                spinnerVideoDetails.setVisibility(View.VISIBLE);
                break;
            case Player.STATE_ENDED:
                // Activate the force enable
                break;
            case Player.STATE_IDLE:
                break;
            case Player.STATE_READY:
                spinnerVideoDetails.setVisibility(View.GONE);
                break;
            default:
                // status = PlaybackStatus.IDLE;
                break;
        }
    }
    @Override
    public void onRepeatModeChanged(int repeatMode) {
    }
    @Override
    public void onShuffleModeEnabledChanged(boolean shuffleModeEnabled) {
    }
    @Override
    public void onPlayerError(ExoPlaybackException error) {
    }
    @Override
    public void onPositionDiscontinuity(int reason) {
    }
    @Override
    public void onPlaybackParametersChanged(PlaybackParameters playbackParameters) {
    }
    @Override
    public void onSeekProcessed() {
    }
Exoplayer is a very advanced library. Even writing a bare minimum would take 40-50 lines of code. So if you really wanna use a sword to chop onions, here is a direct copy pasta :
//manifest.xml 
<manifest ...>
  <uses-permission android:name="android.permission.INTERNET"/>
  <application
    android:usesCleartextTraffic="true"
    ...>
    ...
  </application>
</manifest>
//app/build.gradle
apply plugin: 'com.android.application'
android {
    ...
    compileOptions {
        sourceCompatibility = 1.8
        targetCompatibility = 1.8
    }
}
dependencies {
    ...
    implementation 'com.google.android.exoplayer:exoplayer:2.10.4'
}
    protected void onCreate(Bundle savedInstanceState) {
        ...
        Context ctx =this;
        String CONTENT_URL = "https://www.radiantmediaplayer.com/media/bbb-360p.mp4";
        int playerID=R.id.pv_main;
        int appNameStringRes = R.string.app_name;
        startPlayingVideo(this,CONTENT_URL,playerID,appNameStringRes);
    }
    //
    private void startPlayingVideo(Context ctx , String CONTENT_URL, int playerID, String appNameRes) {
        PlayerView pvMain = ctx.findViewById(playerID);
        //BandwidthMeter bandwidthMeter = new DefaultBandwidthMeter();
        //TrackSelection.Factory videoTrackSelectionFactory = new AdaptiveTrackSelection.Factory(bandwidthMeter);        
        //TrackSelector trackSelectorDef = new DefaultTrackSelector(videoTrackSelectionFactory);
        TrackSelector trackSelectorDef = new DefaultTrackSelector();
        SimpleExoPlayer absPlayerInternal = ExoPlayerFactory.newSimpleInstance(ctx, trackSelectorDef);
        String userAgent = Util.getUserAgent(ctx, ctx.getString(appNameRes));
        DefaultDataSourceFactory defdataSourceFactory = new DefaultDataSourceFactory(ctx,userAgent);
        Uri uriOfContentUrl = Uri.parse(CONTENT_URL);
        MediaSource mediaSource = new ProgressiveMediaSource.Factory(defdataSourceFactory).createMediaSource(uriOfContentUrl);
        absPlayerInternal.prepare(mediaSource);
        absPlayerInternal.setPlayWhenReady(true);
        pvMain.setPlayer(absPlayerInternal);
    }
    private void stopPlayer(PlayerView pv,SimpleExoPlayer absPlayer){
        pv.setPlayer(null);
        absPlayer.release();
        absPlayer = null;
    }
simply add the player view in your activity layout, call the startPlayingVideo(...) in onCreate() and stopPlayer() in the onStop() . I am not an expert but i can try explaining this if you want, but you asked for no complicated stuff, so here is just the code  
The ExoMedia library wraps exoplayer in simpler api and provides a video view for use in layouts. See usage examples on github: https://github.com/brianwernick/ExoMedia/