Android MediaPlayer getCurrentPosition move up and down?

        //audio total 6600ms

    MediaPlayer mPlayer = new MediaPlayer();
    mPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC);
    setVolumeControlStream(AudioManager.STREAM_MUSIC);
    try {
        mPlayer.setDataSource(mFilePath);
        mPlayer.prepare();
        mPlayer.start();
        mPb_record.setMax(mDuration);
        mPb_record.setProgress(0);

        // update progress
        pbHandler.postDelayed(pbRunnable, 100);

        mPlayer.setOnCompletionListener(new OnCompletionListener() {
            @Override
            public void onCompletion(MediaPlayer mp) {
                // TODO ...
            }
        });
    } catch (Exception e) {
        e.printStackTrace();
    }

    Runnable pbRunnable = new Runnable() {
        @Override
        public void run() {
            if (mPlayer != null) {
                System.out.println("CurrentPosition()--   " + mPlayer.getCurrentPosition());

                mPb_record.setProgress(mPlayer.getCurrentPosition());
                pbHandler.postDelayed(this, 100);
            }
        }
    };

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6557 > 6504..so progress show goback ... Why?

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Log

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• 12-30 20:48:56.428: I/System.out(2976): CurrentPosition()---- 6139


• 12-30 20:48:56.528: I/System.out(2976): CurrentPosition()---- 6243


• 12-30 20:48:56.668: I/System.out(2976): CurrentPosition()---- 6348


• 12-30 20:48:56.768: I/System.out(2976): CurrentPosition()---- 6452


• 12-30 20:48:56.868: I/System.out(2976): CurrentPosition()---- 6557


• 12-30 20:48:56.968: I/System.out(2976): CurrentPosition()---- 6504 -- why?


• 12-30 20:48:56.968: I/System.out(2976): CurrentPosition()---- 6504

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