[Chromecast] Wait before starting AudioTrack playback until data is available

This removes the call to start() at the end of init(), and instead
waits until data is fed in. At that time, it writes as much data as
the AudioTrack instance takes, then calls start(), then feeds in any
additional data not taken on the first call.

Bug: internal b/62923451
Test: run on IMX7, observe logs for playback of TTS and Media
      streams, notice no underruns reported

Change-Id: I89b272655176d22e0cb17e896fe6b9c1daa3e717
Reviewed-on: https://chromium-review.googlesource.com/545262Reviewed-by: Luke Halliwell <halliwell@chromium.org>
Commit-Queue: Chris Kuiper <ckuiper@chromium.org>
Cr-Commit-Position: refs/heads/master@{#481915}

chromecast/media/cma/backend/android/java/src/org/chromium/chromecast/cma/backend/android/AudioSinkAudioTrackImpl.java

@@ -151,9 +151,6 @@ class AudioSinkAudioTrackImpl {
         nativeCacheDirectBufferAddress(
                 mNativeAudioSinkAudioTrackImpl, mPcmBuffer, mRenderingDelayBuffer);
 
-        // Put into PLAYING state so it starts playing right when data is fed in.
-        play();
-
         mIsInitialized = true;
     }
 
@@ -180,6 +177,10 @@ class AudioSinkAudioTrackImpl {
         }
     }
 
+    private boolean isStopped() {
+        return mAudioTrack.getPlayState() == AudioTrack.PLAYSTATE_STOPPED;
+    }
+
     private boolean isPlaying() {
         return mAudioTrack.getPlayState() == AudioTrack.PLAYSTATE_PLAYING;
     }
@@ -247,6 +248,32 @@ class AudioSinkAudioTrackImpl {
         long beforeMsecs = SystemClock.elapsedRealtime();
         int bytesWritten = mAudioTrack.write(mPcmBuffer, sizeInBytes, AudioTrack.WRITE_BLOCKING);
 
+        if (bytesWritten < 0) {
+            int error = bytesWritten;
+            Log.e(TAG, "Couldn't write into AudioTrack (" + error + ")");
+            return error;
+        }
+
+        if (isStopped()) {
+            // Data was written, start playing now.
+            play();
+
+            // If not all data fit on the previous write() call (since we were not in PLAYING state
+            // it didn't block), do a second (now blocking) call to write().
+            int bytesLeft = sizeInBytes - bytesWritten;
+            if (bytesLeft > 0) {
+                mPcmBuffer.position(bytesWritten);
+                int moreBytesWritten =
+                        mAudioTrack.write(mPcmBuffer, bytesLeft, AudioTrack.WRITE_BLOCKING);
+                if (moreBytesWritten < 0) {
+                    int error = moreBytesWritten;
+                    Log.e(TAG, "Couldn't write into AudioTrack (" + error + ")");
+                    return error;
+                }
+                bytesWritten += moreBytesWritten;
+            }
+        }
+
         int framesWritten = bytesWritten / BYTES_PER_FRAME;
         mTotalFramesWritten += framesWritten;
 
@@ -257,10 +284,9 @@ class AudioSinkAudioTrackImpl {
                             + " took:" + (SystemClock.elapsedRealtime() - beforeMsecs) + "ms");
         }
 
-        if (bytesWritten <= 0 || isPaused()) {
-            // Either hit an error or we are in PAUSED state, in which case the
-            // write() is non-blocking. If not all data was written, we will come
-            // back here once we transition back into PLAYING state.
+        if (bytesWritten < sizeInBytes && isPaused()) {
+            // We are in PAUSED state, in which case the write() is non-blocking. If not all data
+            // was written, we will come back here once we transition back into PLAYING state.
             return bytesWritten;
         }