https://source.android.com/ 
/*
 * Copyright (C) 2015 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.media;

import android.annotation.IntDef;
import android.annotation.NonNull;
import android.annotation.Nullable;
import android.media.AudioTrack;
import android.media.PlaybackParams;
import android.os.Handler;
import android.os.Looper;
import android.os.Message;
import android.util.Log;
import android.view.Surface;

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.nio.ByteBuffer;
import java.util.concurrent.TimeUnit;
import java.util.LinkedList;
import java.util.List;


MediaSync class can be used to synchronously play audio and video streams.
It can be used to play audio-only or video-only stream, too.

MediaSync is generally used like this:

MediaSync sync = new MediaSync(); sync.setSurface(surface); Surface inputSurface = sync.createInputSurface(); ... // MediaCodec videoDecoder = ...; videoDecoder.configure(format, inputSurface, ...); ... sync.setAudioTrack(audioTrack); sync.setCallback(new MediaSync.Callback() { @Override public void onAudioBufferConsumed(MediaSync sync, ByteBuffer audioBuffer, int bufferId) { ... } }, null); // This needs to be done since sync is paused on creation. sync.setPlaybackParams(new PlaybackParams().setSpeed(1.f)); for (;;) { ... // send video frames to surface for rendering, e.g., call // videoDecoder.releaseOutputBuffer(videoOutputBufferIx, videoPresentationTimeNs); // More details are available as below. ... sync.queueAudio(audioByteBuffer, bufferId, audioPresentationTimeUs); // non-blocking. // The audioByteBuffer and bufferId will be returned via callback. // More details are available as below. ... ... } sync.setPlaybackParams(new PlaybackParams().setSpeed(0.f)); sync.release(); sync = null; // The following code snippet illustrates how video/audio raw frames are created by // MediaCodec's, how they are fed to MediaSync and how they are returned by MediaSync. // This is the callback from MediaCodec. onOutputBufferAvailable(MediaCodec codec, int bufferId, BufferInfo info) { // ... if (codec == videoDecoder) { // surface timestamp must contain media presentation time in nanoseconds. codec.releaseOutputBuffer(bufferId, 1000 * info.presentationTime); } else { ByteBuffer audioByteBuffer = codec.getOutputBuffer(bufferId); sync.queueAudio(audioByteBuffer, bufferId, info.presentationTime); } // ... } // This is the callback from MediaSync. onAudioBufferConsumed(MediaSync sync, ByteBuffer buffer, int bufferId) { // ... audioDecoder.releaseBuffer(bufferId, false); // ... } 

The client needs to configure corresponding sink by setting the Surface and/or AudioTrack
based on the stream type it will play.

 For video, the client needs to call createInputSurface to obtain a surface on which it will render video frames. 
 For audio, the client needs to set up audio track correctly, e.g., using AudioTrack.MODE_STREAM. The audio buffers are sent to MediaSync directly via queueAudio, and are returned to the client via Callback.onAudioBufferConsumed asynchronously. The client should not modify an audio buffer till it's returned. 

The client can optionally pre-fill audio/video buffers by setting playback rate to 0.0,
and then feed audio/video buffers to corresponding components. This can reduce possible
initial underrun.



/**
 * MediaSync class can be used to synchronously play audio and video streams.
 * It can be used to play audio-only or video-only stream, too.
 *
 * <p>MediaSync is generally used like this:
 * <pre>
 * MediaSync sync = new MediaSync();
 * sync.setSurface(surface);
 * Surface inputSurface = sync.createInputSurface();
 * ...
 * // MediaCodec videoDecoder = ...;
 * videoDecoder.configure(format, inputSurface, ...);
 * ...
 * sync.setAudioTrack(audioTrack);
 * sync.setCallback(new MediaSync.Callback() {
 *     {@literal @Override}
 *     public void onAudioBufferConsumed(MediaSync sync, ByteBuffer audioBuffer, int bufferId) {
 *         ...
 *     }
 * }, null);
 * // This needs to be done since sync is paused on creation.
 * sync.setPlaybackParams(new PlaybackParams().setSpeed(1.f));
 *
 * for (;;) {
 *   ...
 *   // send video frames to surface for rendering, e.g., call
 *   // videoDecoder.releaseOutputBuffer(videoOutputBufferIx, videoPresentationTimeNs);
 *   // More details are available as below.
 *   ...
 *   sync.queueAudio(audioByteBuffer, bufferId, audioPresentationTimeUs); // non-blocking.
 *   // The audioByteBuffer and bufferId will be returned via callback.
 *   // More details are available as below.
 *   ...
 *     ...
 * }
 * sync.setPlaybackParams(new PlaybackParams().setSpeed(0.f));
 * sync.release();
 * sync = null;
 *
 * // The following code snippet illustrates how video/audio raw frames are created by
 * // MediaCodec's, how they are fed to MediaSync and how they are returned by MediaSync.
 * // This is the callback from MediaCodec.
 * onOutputBufferAvailable(MediaCodec codec, int bufferId, BufferInfo info) {
 *     // ...
 *     if (codec == videoDecoder) {
 *         // surface timestamp must contain media presentation time in nanoseconds.
 *         codec.releaseOutputBuffer(bufferId, 1000 * info.presentationTime);
 *     } else {
 *         ByteBuffer audioByteBuffer = codec.getOutputBuffer(bufferId);
 *         sync.queueAudio(audioByteBuffer, bufferId, info.presentationTime);
 *     }
 *     // ...
 * }
 *
 * // This is the callback from MediaSync.
 * onAudioBufferConsumed(MediaSync sync, ByteBuffer buffer, int bufferId) {
 *     // ...
 *     audioDecoder.releaseBuffer(bufferId, false);
 *     // ...
 * }
 *
 * </pre>
 *
 * The client needs to configure corresponding sink by setting the Surface and/or AudioTrack
 * based on the stream type it will play.
 * <p>
 * For video, the client needs to call {@link #createInputSurface} to obtain a surface on
 * which it will render video frames.
 * <p>
 * For audio, the client needs to set up audio track correctly, e.g., using {@link
 * AudioTrack#MODE_STREAM}. The audio buffers are sent to MediaSync directly via {@link
 * #queueAudio}, and are returned to the client via {@link Callback#onAudioBufferConsumed}
 * asynchronously. The client should not modify an audio buffer till it's returned.
 * <p>
 * The client can optionally pre-fill audio/video buffers by setting playback rate to 0.0,
 * and then feed audio/video buffers to corresponding components. This can reduce possible
 * initial underrun.
 * <p>
 */
public final class MediaSync {
    
MediaSync callback interface. Used to notify the user asynchronously
of various MediaSync events.

/**
     * MediaSync callback interface. Used to notify the user asynchronously
     * of various MediaSync events.
     */
    public static abstract class Callback {
        
Called when returning an audio buffer which has been consumed.

Params:
  • sync – The MediaSync object.
  • audioBuffer – The returned audio buffer.
  • bufferId – The ID associated with audioBuffer as passed into MediaSync.queueAudio.
/**
         * Called when returning an audio buffer which has been consumed.
         *
         * @param sync The MediaSync object.
         * @param audioBuffer The returned audio buffer.
         * @param bufferId The ID associated with audioBuffer as passed into
         *     {@link MediaSync#queueAudio}.
         */
        public abstract void onAudioBufferConsumed(
                @NonNull MediaSync sync, @NonNull ByteBuffer audioBuffer, int bufferId);
    }

    
Audio track failed.

See Also:
  • OnErrorListener
/** Audio track failed.
     * @see android.media.MediaSync.OnErrorListener
     */
    public static final int MEDIASYNC_ERROR_AUDIOTRACK_FAIL = 1;

    
The surface failed to handle video buffers.

See Also:
  • OnErrorListener
/** The surface failed to handle video buffers.
     * @see android.media.MediaSync.OnErrorListener
     */
    public static final int MEDIASYNC_ERROR_SURFACE_FAIL = 2;

    
Interface definition of a callback to be invoked when there
has been an error during an asynchronous operation (other errors
will throw exceptions at method call time).

/**
     * Interface definition of a callback to be invoked when there
     * has been an error during an asynchronous operation (other errors
     * will throw exceptions at method call time).
     */
    public interface OnErrorListener {
        
Called to indicate an error.

Params:
/**
         * Called to indicate an error.
         *
         * @param sync The MediaSync the error pertains to
         * @param what The type of error that has occurred:
         * <ul>
         * <li>{@link #MEDIASYNC_ERROR_AUDIOTRACK_FAIL}
         * <li>{@link #MEDIASYNC_ERROR_SURFACE_FAIL}
         * </ul>
         * @param extra an extra code, specific to the error. Typically
         * implementation dependent.
         */
        void onError(@NonNull MediaSync sync, int what, int extra);
    }

    private static final String TAG = "MediaSync";

    private static final int EVENT_CALLBACK = 1;
    private static final int EVENT_SET_CALLBACK = 2;

    private static final int CB_RETURN_AUDIO_BUFFER = 1;

    private static class AudioBuffer {
        public ByteBuffer mByteBuffer;
        public int mBufferIndex;
        long mPresentationTimeUs;

        public AudioBuffer(@NonNull ByteBuffer byteBuffer, int bufferId,
                           long presentationTimeUs) {
            mByteBuffer = byteBuffer;
            mBufferIndex = bufferId;
            mPresentationTimeUs = presentationTimeUs;
        }
    }

    private final Object mCallbackLock = new Object();
    private Handler mCallbackHandler = null;
    private MediaSync.Callback mCallback = null;

    private final Object mOnErrorListenerLock = new Object();
    private Handler mOnErrorListenerHandler = null;
    private MediaSync.OnErrorListener mOnErrorListener = null;

    private Thread mAudioThread = null;
    // Created on mAudioThread when mAudioThread is started. When used on user thread, they should
    // be guarded by checking mAudioThread.
    private Handler mAudioHandler = null;
    private Looper mAudioLooper = null;

    private final Object mAudioLock = new Object();
    private AudioTrack mAudioTrack = null;
    private List<AudioBuffer> mAudioBuffers = new LinkedList<AudioBuffer>();
    // this is only used for paused/running decisions, so it is not affected by clock drift
    private float mPlaybackRate = 0.0f;

    private long mNativeContext;

    
Class constructor. On creation, MediaSync is paused, i.e., playback rate is 0.0f.

/**
     * Class constructor. On creation, MediaSync is paused, i.e., playback rate is 0.0f.
     */
    public MediaSync() {
        native_setup();
    }

    private native final void native_setup();

    @Override
    protected void finalize() {
        native_finalize();
    }

    private native final void native_finalize();

    
Make sure you call this when you're done to free up any opened
component instance instead of relying on the garbage collector
to do this for you at some point in the future.

/**
     * Make sure you call this when you're done to free up any opened
     * component instance instead of relying on the garbage collector
     * to do this for you at some point in the future.
     */
    public final void release() {
        returnAudioBuffers();
        if (mAudioThread != null) {
            if (mAudioLooper != null) {
                mAudioLooper.quit();
            }
        }
        setCallback(null, null);
        native_release();
    }

    private native final void native_release();

    
Sets an asynchronous callback for actionable MediaSync events.


This method can be called multiple times to update a previously set callback. If the
handler is changed, undelivered notifications scheduled for the old handler may be dropped.


Do not call this inside callback.

Params:
  • cb – The callback that will run. Use null to stop receiving callbacks.
  • handler – The Handler that will run the callback. Use null to use MediaSync's internal handler if it exists.
/**
     * Sets an asynchronous callback for actionable MediaSync events.
     * <p>
     * This method can be called multiple times to update a previously set callback. If the
     * handler is changed, undelivered notifications scheduled for the old handler may be dropped.
     * <p>
     * <b>Do not call this inside callback.</b>
     *
     * @param cb The callback that will run. Use {@code null} to stop receiving callbacks.
     * @param handler The Handler that will run the callback. Use {@code null} to use MediaSync's
     *     internal handler if it exists.
     */
    public void setCallback(@Nullable /* MediaSync. */ Callback cb, @Nullable Handler handler) {
        synchronized(mCallbackLock) {
            if (handler != null) {
                mCallbackHandler = handler;
            } else {
                Looper looper;
                if ((looper = Looper.myLooper()) == null) {
                    looper = Looper.getMainLooper();
                }
                if (looper == null) {
                    mCallbackHandler = null;
                } else {
                    mCallbackHandler = new Handler(looper);
                }
            }

            mCallback = cb;
        }
    }

    
Sets an asynchronous callback for error events.


This method can be called multiple times to update a previously set listener. If the
handler is changed, undelivered notifications scheduled for the old handler may be dropped.


Do not call this inside callback.

Params:
  • listener – The callback that will run. Use null to stop receiving callbacks.
  • handler – The Handler that will run the callback. Use null to use MediaSync's internal handler if it exists.
/**
     * Sets an asynchronous callback for error events.
     * <p>
     * This method can be called multiple times to update a previously set listener. If the
     * handler is changed, undelivered notifications scheduled for the old handler may be dropped.
     * <p>
     * <b>Do not call this inside callback.</b>
     *
     * @param listener The callback that will run. Use {@code null} to stop receiving callbacks.
     * @param handler The Handler that will run the callback. Use {@code null} to use MediaSync's
     *     internal handler if it exists.
     */
    public void setOnErrorListener(@Nullable /* MediaSync. */ OnErrorListener listener,
            @Nullable Handler handler) {
        synchronized(mOnErrorListenerLock) {
            if (handler != null) {
                mOnErrorListenerHandler = handler;
            } else {
                Looper looper;
                if ((looper = Looper.myLooper()) == null) {
                    looper = Looper.getMainLooper();
                }
                if (looper == null) {
                    mOnErrorListenerHandler = null;
                } else {
                    mOnErrorListenerHandler = new Handler(looper);
                }
            }

            mOnErrorListener = listener;
        }
    }

    
Sets the output surface for MediaSync.


Currently, this is only supported in the Initialized state.

Params:
  • surface – Specify a surface on which to render the video data.
Throws:
  • IllegalArgumentException – if the surface has been released, is invalid,
    or can not be connected.
  • IllegalStateException – if setting the surface is not supported, e.g.
    not in the Initialized state, or another surface has already been set.
/**
     * Sets the output surface for MediaSync.
     * <p>
     * Currently, this is only supported in the Initialized state.
     *
     * @param surface Specify a surface on which to render the video data.
     * @throws IllegalArgumentException if the surface has been released, is invalid,
     *     or can not be connected.
     * @throws IllegalStateException if setting the surface is not supported, e.g.
     *     not in the Initialized state, or another surface has already been set.
     */
    public void setSurface(@Nullable Surface surface) {
        native_setSurface(surface);
    }

    private native final void native_setSurface(@Nullable Surface surface);

    
Sets the audio track for MediaSync.


Currently, this is only supported in the Initialized state.

Params:
  • audioTrack – Specify an AudioTrack through which to render the audio data.
Throws:
  • IllegalArgumentException – if the audioTrack has been released, or is invalid.
  • IllegalStateException – if setting the audio track is not supported, e.g.
    not in the Initialized state, or another audio track has already been set.
/**
     * Sets the audio track for MediaSync.
     * <p>
     * Currently, this is only supported in the Initialized state.
     *
     * @param audioTrack Specify an AudioTrack through which to render the audio data.
     * @throws IllegalArgumentException if the audioTrack has been released, or is invalid.
     * @throws IllegalStateException if setting the audio track is not supported, e.g.
     *     not in the Initialized state, or another audio track has already been set.
     */
    public void setAudioTrack(@Nullable AudioTrack audioTrack) {
        native_setAudioTrack(audioTrack);
        mAudioTrack = audioTrack;
        if (audioTrack != null && mAudioThread == null) {
            createAudioThread();
        }
    }

    private native final void native_setAudioTrack(@Nullable AudioTrack audioTrack);

    
Requests a Surface to use as the input. This may only be called after setSurface. 

The application is responsible for calling release() on the Surface when
done.

Throws:
/**
     * Requests a Surface to use as the input. This may only be called after
     * {@link #setSurface}.
     * <p>
     * The application is responsible for calling release() on the Surface when
     * done.
     * @throws IllegalStateException if not set, or another input surface has
     *     already been created.
     */
    @NonNull
    public native final Surface createInputSurface();

    
Sets playback rate using PlaybackParams. 
 When using MediaSync with AudioTrack, set playback params using this call instead of calling it directly on the track, so that the sync is aware of the params change. 

This call also works if there is no audio track.

Params:
  • params – the playback params to use. 
    Speed is the ratio between desired playback rate and normal one. 1.0 means normal playback speed. 0.0 means pause. Value larger than 1.0 means faster playback, while value between 0.0 and 1.0 for slower playback. Note: the normal rate
    does not change as a result of this call. To restore the original rate at any time,
    use speed of 1.0.
Throws:
/**
     * Sets playback rate using {@link PlaybackParams}.
     * <p>
     * When using MediaSync with {@link AudioTrack}, set playback params using this
     * call instead of calling it directly on the track, so that the sync is aware of
     * the params change.
     * <p>
     * This call also works if there is no audio track.
     *
     * @param params the playback params to use. {@link PlaybackParams#getSpeed
     *     Speed} is the ratio between desired playback rate and normal one. 1.0 means
     *     normal playback speed. 0.0 means pause. Value larger than 1.0 means faster playback,
     *     while value between 0.0 and 1.0 for slower playback. <b>Note:</b> the normal rate
     *     does not change as a result of this call. To restore the original rate at any time,
     *     use speed of 1.0.
     *
     * @throws IllegalStateException if the internal sync engine or the audio track has not
     *     been initialized.
     * @throws IllegalArgumentException if the params are not supported.
     */
    public void setPlaybackParams(@NonNull PlaybackParams params) {
        synchronized(mAudioLock) {
            mPlaybackRate = native_setPlaybackParams(params);;
        }
        if (mPlaybackRate != 0.0 && mAudioThread != null) {
            postRenderAudio(0);
        }
    }

    
Gets the playback rate using PlaybackParams. 
Throws:
Returns:the playback rate being used.
/**
     * Gets the playback rate using {@link PlaybackParams}.
     *
     * @return the playback rate being used.
     *
     * @throws IllegalStateException if the internal sync engine or the audio track has not
     *     been initialized.
     */
    @NonNull
    public native PlaybackParams getPlaybackParams();

    private native float native_setPlaybackParams(@NonNull PlaybackParams params);

    
Sets A/V sync mode.

Params:
  • params – the A/V sync params to apply
Throws:
/**
     * Sets A/V sync mode.
     *
     * @param params the A/V sync params to apply
     *
     * @throws IllegalStateException if the internal player engine has not been
     * initialized.
     * @throws IllegalArgumentException if params are not supported.
     */
    public void setSyncParams(@NonNull SyncParams params) {
        synchronized(mAudioLock) {
            mPlaybackRate = native_setSyncParams(params);;
        }
        if (mPlaybackRate != 0.0 && mAudioThread != null) {
            postRenderAudio(0);
        }
    }

    private native float native_setSyncParams(@NonNull SyncParams params);

    
Gets the A/V sync mode.

Throws:
Returns:the A/V sync params
/**
     * Gets the A/V sync mode.
     *
     * @return the A/V sync params
     *
     * @throws IllegalStateException if the internal player engine has not been
     * initialized.
     */
    @NonNull
    public native SyncParams getSyncParams();

    
Flushes all buffers from the sync object.


All pending unprocessed audio and video buffers are discarded. If an audio track was
configured, it is flushed and stopped. If a video output surface was configured, the
last frame queued to it is left on the frame. Queue a blank video frame to clear the
surface,


No callbacks are received for the flushed buffers.

Throws:
  • IllegalStateException – if the internal player engine has not been
initialized.
/**
     * Flushes all buffers from the sync object.
     * <p>
     * All pending unprocessed audio and video buffers are discarded. If an audio track was
     * configured, it is flushed and stopped. If a video output surface was configured, the
     * last frame queued to it is left on the frame. Queue a blank video frame to clear the
     * surface,
     * <p>
     * No callbacks are received for the flushed buffers.
     *
     * @throws IllegalStateException if the internal player engine has not been
     * initialized.
     */
    public void flush() {
        synchronized(mAudioLock) {
            mAudioBuffers.clear();
            mCallbackHandler.removeCallbacksAndMessages(null);
        }
        if (mAudioTrack != null) {
            mAudioTrack.pause();
            mAudioTrack.flush();
            // Call stop() to signal to the AudioSink to completely fill the
            // internal buffer before resuming playback.
            mAudioTrack.stop();
        }
        native_flush();
    }

    private native final void native_flush();

    
Get current playback position.


The MediaTimestamp represents how the media time correlates to the system time in
a linear fashion using an anchor and a clock rate. During regular playback, the media
time moves fairly constantly (though the anchor frame may be rebased to a current
system time, the linear correlation stays steady). Therefore, this method does not
need to be called often.

 To help users get current playback position, this method always anchors the timestamp to the current system time, so MediaTimestamp.getAnchorMediaTimeUs can be used as current playback position. 
See Also:
Returns:a MediaTimestamp object if a timestamp is available, or null if no timestamp is available, e.g. because the media player has not been initialized.
/**
     * Get current playback position.
     * <p>
     * The MediaTimestamp represents how the media time correlates to the system time in
     * a linear fashion using an anchor and a clock rate. During regular playback, the media
     * time moves fairly constantly (though the anchor frame may be rebased to a current
     * system time, the linear correlation stays steady). Therefore, this method does not
     * need to be called often.
     * <p>
     * To help users get current playback position, this method always anchors the timestamp
     * to the current {@link System#nanoTime system time}, so
     * {@link MediaTimestamp#getAnchorMediaTimeUs} can be used as current playback position.
     *
     * @return a MediaTimestamp object if a timestamp is available, or {@code null} if no timestamp
     *         is available, e.g. because the media player has not been initialized.
     *
     * @see MediaTimestamp
     */
    @Nullable
    public MediaTimestamp getTimestamp()
    {
        try {
            // TODO: create the timestamp in native
            MediaTimestamp timestamp = new MediaTimestamp();
            if (native_getTimestamp(timestamp)) {
                return timestamp;
            } else {
                return null;
            }
        } catch (IllegalStateException e) {
            return null;
        }
    }

    private native final boolean native_getTimestamp(@NonNull MediaTimestamp timestamp);

    
Queues the audio data asynchronously for playback (AudioTrack must be in streaming mode). If the audio track was flushed as a result of flush, it will be restarted. 
Params:
  • audioData – the buffer that holds the data to play. This buffer will be returned
    to the client via registered callback.
  • bufferId – an integer used to identify audioData. It will be returned to
    the client along with audioData. This helps applications to keep track of audioData,
    e.g., it can be used to store the output buffer index used by the audio codec.
  • presentationTimeUs – the presentation timestamp in microseconds for the first frame
    in the buffer.
Throws:
  • IllegalStateException – if audio track is not set or internal configureation
    has not been done correctly.
/**
     * Queues the audio data asynchronously for playback (AudioTrack must be in streaming mode).
     * If the audio track was flushed as a result of {@link #flush}, it will be restarted.
     * @param audioData the buffer that holds the data to play. This buffer will be returned
     *     to the client via registered callback.
     * @param bufferId an integer used to identify audioData. It will be returned to
     *     the client along with audioData. This helps applications to keep track of audioData,
     *     e.g., it can be used to store the output buffer index used by the audio codec.
     * @param presentationTimeUs the presentation timestamp in microseconds for the first frame
     *     in the buffer.
     * @throws IllegalStateException if audio track is not set or internal configureation
     *     has not been done correctly.
     */
    public void queueAudio(
            @NonNull ByteBuffer audioData, int bufferId, long presentationTimeUs) {
        if (mAudioTrack == null || mAudioThread == null) {
            throw new IllegalStateException(
                    "AudioTrack is NOT set or audio thread is not created");
        }

        synchronized(mAudioLock) {
            mAudioBuffers.add(new AudioBuffer(audioData, bufferId, presentationTimeUs));
        }

        if (mPlaybackRate != 0.0) {
            postRenderAudio(0);
        }
    }

    // When called on user thread, make sure to check mAudioThread != null.
    private void postRenderAudio(long delayMillis) {
        mAudioHandler.postDelayed(new Runnable() {
            public void run() {
                synchronized(mAudioLock) {
                    if (mPlaybackRate == 0.0) {
                        return;
                    }

                    if (mAudioBuffers.isEmpty()) {
                        return;
                    }

                    AudioBuffer audioBuffer = mAudioBuffers.get(0);
                    int size = audioBuffer.mByteBuffer.remaining();
                    // restart audio track after flush
                    if (size > 0 && mAudioTrack.getPlayState() != AudioTrack.PLAYSTATE_PLAYING) {
                        try {
                            mAudioTrack.play();
                        } catch (IllegalStateException e) {
                            Log.w(TAG, "could not start audio track");
                        }
                    }
                    int sizeWritten = mAudioTrack.write(
                            audioBuffer.mByteBuffer,
                            size,
                            AudioTrack.WRITE_NON_BLOCKING);
                    if (sizeWritten > 0) {
                        if (audioBuffer.mPresentationTimeUs != -1) {
                            native_updateQueuedAudioData(
                                    size, audioBuffer.mPresentationTimeUs);
                            audioBuffer.mPresentationTimeUs = -1;
                        }

                        if (sizeWritten == size) {
                            postReturnByteBuffer(audioBuffer);
                            mAudioBuffers.remove(0);
                            if (!mAudioBuffers.isEmpty()) {
                                postRenderAudio(0);
                            }
                            return;
                        }
                    }
                    long pendingTimeMs = TimeUnit.MICROSECONDS.toMillis(
                            native_getPlayTimeForPendingAudioFrames());
                    postRenderAudio(pendingTimeMs / 2);
                }
            }
        }, delayMillis);
    }

    private native final void native_updateQueuedAudioData(
            int sizeInBytes, long presentationTimeUs);

    private native final long native_getPlayTimeForPendingAudioFrames();

    private final void postReturnByteBuffer(@NonNull final AudioBuffer audioBuffer) {
        synchronized(mCallbackLock) {
            if (mCallbackHandler != null) {
                final MediaSync sync = this;
                mCallbackHandler.post(new Runnable() {
                    public void run() {
                        Callback callback;
                        synchronized(mCallbackLock) {
                            callback = mCallback;
                            if (mCallbackHandler == null
                                    || mCallbackHandler.getLooper().getThread()
                                            != Thread.currentThread()) {
                                // callback handler has been changed.
                                return;
                            }
                        }
                        if (callback != null) {
                            callback.onAudioBufferConsumed(sync, audioBuffer.mByteBuffer,
                                    audioBuffer.mBufferIndex);
                        }
                    }
                });
            }
        }
    }

    private final void returnAudioBuffers() {
        synchronized(mAudioLock) {
            for (AudioBuffer audioBuffer: mAudioBuffers) {
                postReturnByteBuffer(audioBuffer);
            }
            mAudioBuffers.clear();
        }
    }

    private void createAudioThread() {
        mAudioThread = new Thread() {
            @Override
            public void run() {
                Looper.prepare();
                synchronized(mAudioLock) {
                    mAudioLooper = Looper.myLooper();
                    mAudioHandler = new Handler();
                    mAudioLock.notify();
                }
                Looper.loop();
            }
        };
        mAudioThread.start();

        synchronized(mAudioLock) {
            try {
                mAudioLock.wait();
            } catch(InterruptedException e) {
            }
        }
    }

    static {
        System.loadLibrary("media_jni");
        native_init();
    }

    private static native final void native_init();
}