音视频：19.FFmpeg-视频加背景音乐、H.264协议

具体代码请看：NDKPractice项目的ffmpeg88livepush

1.实现视频加背景音乐

    private MediaInfoListener mMediaInfoListener = new MediaInfoListener() {
   
        private long mAudioPts = 0;
        private int mSampleRate = 0;
        private int mChannels = 0;

        @Override
        public void musicInfo(int sampleRate, int channels) {
   
            // 获取了音频的信息
            try {
   
                initAudioCodec(sampleRate, channels);
            } catch (Exception e) {
   
                e.printStackTrace();
            }
            this.mSampleRate = sampleRate;
            this.mChannels = channels;
        }

        @Override
        public void callbackPcm(byte[] pcmData, int size) {
   
            // 把数据写入到 mAudioCodec 的 InputBuffer
            int inputBufferIndex = mAudioCodec.dequeueInputBuffer(0);
            if (inputBufferIndex >= 0) {
   
                ByteBuffer byteBuffer = mAudioCodec.getInputBuffers()[inputBufferIndex];
                byteBuffer.clear();
                byteBuffer.put(pcmData);

                // pts  44100 * 2 *2
                mAudioPts += size * 1000000 / mSampleRate * mChannels * 2;
                // size 22050*2*2
                mAudioCodec.queueInputBuffer(inputBufferIndex, 0, size, mAudioPts, 0);
            }
        }
    };
    
    /**
     * 音频的编码线程
     */
    private static final class AudioEncoderThread extends Thread {
   
        private final MediaMuxer mMediaMuxer;
        private WeakReference<BaseVideoRecorder> mVideoRecorderWr;
        private volatile boolean mShouldExit = false;
        private MediaCodec mAudioCodec;
        private MediaCodec.BufferInfo mBufferInfo;
        private int mAudioTrackIndex = -1;
        private long mAudioPts = 0;
        private final CyclicBarrier mStartCb