[android] Handle mediacodec callback with a handler thread

Now the MediaCodec callbacks and the activity lifecycle callbacks
are called on the main thread. When pausing YouTube, the MediaCodec
callbacks may be blocked until the lifecycle callbacks are done.
This may cause frame drops on a resource-limited device when the
MediaCodec callback to notify a newly decoded frame is blocked and
we run out of decoded frames. Running the MediaCodec callbacks on a
handler thread could avoid this problem.

Change-Id: I5ffdb1f5a582c3d01964b3f98c99d7aed211674a

starboard/android/apk/app/src/main/java/dev/cobalt/media/MediaCodecBridge.java

@@ -31,6 +31,8 @@
 import android.media.MediaFormat;
 import android.os.Build;
 import android.os.Bundle;
+import android.os.Handler;
+import android.os.HandlerThread;
 import android.view.Surface;
 import androidx.annotation.Nullable;
 import dev.cobalt.util.Log;
@@ -93,6 +95,9 @@ class MediaCodecBridge {
   // which would cause GC cycles long enough to impact playback.
   private final MediaCodec.BufferInfo info = new MediaCodec.BufferInfo();
 
+  private final Handler mHandler;
+  private final HandlerThread mHandlerThread;
+
   // Type of bitrate adjustment for video encoder.
   public enum BitrateAdjustmentTypes {
     // No adjustment - video encoder has no known bitrate problem.
@@ -461,6 +466,9 @@ private MediaCodecBridge(
     mLastPresentationTimeUs = 0;
     mFlushed = true;
     mBitrateAdjustmentType = bitrateAdjustmentType;
+    mHandlerThread = new HandlerThread("DecodeHandler");
+    mHandlerThread.start();
+    mHandler = new Handler(mHandlerThread.getLooper());
     mCallback =
         new MediaCodec.Callback() {
           @Override
@@ -525,7 +533,7 @@ public void onOutputFormatChanged(MediaCodec codec, MediaFormat format) {
             }
           }
         };
-    mMediaCodec.setCallback(mCallback);
+    mMediaCodec.setCallback(mCallback, mHandler);
 
     // TODO: support OnFrameRenderedListener for non tunnel mode
     if (tunnelModeAudioSessionId != -1) {
@@ -806,6 +814,7 @@ public void release() {
       Log.e(TAG, "Cannot release media codec", e);
     }
     mMediaCodec = null;
+    mHandlerThread.quitSafely();
   }
 
   @SuppressWarnings("unused")