Fix AudoFocus pausing video when attempting to play (#1)

Fix AudioFocus bug that could cause the player to stop responding to play/pause in some instances.

Fixes issue react-native-video#1945

This was caused by the player requesting audio focus on each play (un-pause) and that resulted in a small window of Audio focus loss and then gain. The focus loss results in the player being paused while the player was supposed to play at the time. The solution is to keep track of Audio focus and not request new focus if we already have it.

Author: armands-malejevs

CHANGELOG.md

@@ -1,5 +1,7 @@
 ## Changelog
 
+- Fix Android AudioFocus bug that could cause player to not respond to play/pause in some instances [#2311](https://github.com/react-native-video/react-native-video/pull/2311)
+
 ### Version 5.1.0-alpha9
 
 - Add ARM64 support for windows [#2137](https://github.com/react-native-community/react-native-video/pull/2137)

android-exoplayer/src/main/java/com/brentvatne/exoplayer/ReactExoplayerView.java

@@ -122,6 +122,7 @@ class ReactExoplayerView extends FrameLayout implements
     private boolean isPaused;
     private boolean isBuffering;
     private boolean muted = false;
+    private boolean hasAudioFocus = false;
     private float rate = 1f;
     private float audioVolume = 1f;
     private int minLoadRetryCount = 3;
@@ -567,7 +568,7 @@ private void releasePlayer() {
     }
 
     private boolean requestAudioFocus() {
-        if (disableFocus || srcUri == null) {
+        if (disableFocus || srcUri == null || this.hasAudioFocus) {
             return true;
         }
         int result = audioManager.requestAudioFocus(this,
@@ -582,8 +583,8 @@ private void setPlayWhenReady(boolean playWhenReady) {
         }
 
         if (playWhenReady) {
-            boolean hasAudioFocus = requestAudioFocus();
-            if (hasAudioFocus) {
+            this.hasAudioFocus = requestAudioFocus();
+            if (this.hasAudioFocus) {
                 player.setPlayWhenReady(true);
             }
         } else {
@@ -678,6 +679,7 @@ private HttpDataSource.Factory buildHttpDataSourceFactory(boolean useBandwidthMe
     public void onAudioFocusChange(int focusChange) {
         switch (focusChange) {
             case AudioManager.AUDIOFOCUS_LOSS:
+                this.hasAudioFocus = false;
                 eventEmitter.audioFocusChanged(false);
                 pausePlayback();
                 audioManager.abandonAudioFocus(this);
@@ -686,6 +688,7 @@ public void onAudioFocusChange(int focusChange) {
                 eventEmitter.audioFocusChanged(false);
                 break;
             case AudioManager.AUDIOFOCUS_GAIN:
+                this.hasAudioFocus = true;
                 eventEmitter.audioFocusChanged(true);
                 break;
             default: