Android Studio Mediaplayer如何淡入淡出

Question

我正在 android 工作室使用媒体播放器 class。我只是想淡出一种声音并淡入另一种声音，而不是使用 setVolume(0,0) 和 setVolume(1,1)。

我为此创建了两个媒体播放器，似乎我在这个线程中找到了解决方案：Android: How to create fade-in/fade-out sound effects for any music file that my app plays?但我不知道如何使用 deltaTime。

还有一些其他的解决方案，我几乎看不懂。难道没有一种简单的方法可以让两个媒体播放器交叉淡入淡出，我无法想象还没有人需要这个，或者每个人都使用强迫代码来实现它。我应该如何使用 deltaTime？

Answer 1

查看链接 example，您必须在循环中调用 fadeIn()/fadeOut()，以 increase/decrease 一段时间内的音量。 deltaTime 将是循环每次迭代之间的时间。

您必须在与主 UI 线程不同的线程中执行此操作，以免阻塞它并导致您的应用程序崩溃。您可以通过将此循环放在新的 Thread/Runnable/Timer.

中来做到这一点

这是我的淡入示例（您可以对淡出做类似的事情）：

float volume = 0;

private void startFadeIn(){
    final int FADE_DURATION = 3000; //The duration of the fade
    //The amount of time between volume changes. The smaller this is, the smoother the fade
    final int FADE_INTERVAL = 250;
    final int MAX_VOLUME = 1; //The volume will increase from 0 to 1
    int numberOfSteps = FADE_DURATION/FADE_INTERVAL; //Calculate the number of fade steps
    //Calculate by how much the volume changes each step
    final float deltaVolume = MAX_VOLUME / (float)numberOfSteps;

    //Create a new Timer and Timer task to run the fading outside the main UI thread
    final Timer timer = new Timer(true);
    TimerTask timerTask = new TimerTask() {
        @Override
        public void run() {
            fadeInStep(deltaVolume); //Do a fade step
            //Cancel and Purge the Timer if the desired volume has been reached
            if(volume>=1f){
                timer.cancel();
                timer.purge();
            }
        }
    };

    timer.schedule(timerTask,FADE_INTERVAL,FADE_INTERVAL);
}

private void fadeInStep(float deltaVolume){
    mediaPlayer.setVolume(volume, volume);
    volume += deltaVolume;

}

我不会使用两个单独的 MediaPlayer 对象，在您的情况下，我会只使用一个并在淡入淡出之间交换轨道。示例：

**Audio track #1 is playing but coming to the end**
startFadeOut();
mediaPlayer.stop();
mediaPlayer.reset();
mediaPlayer.setDataSource(context,audiofileUri);
mediaPlayer.prepare();
mediaPlayer.start();
startFadeIn();
**Audio track #2 has faded in and is now playing**

希望这能解决您的问题。

Answer 2

这是淡出代码，以防它可以节省一些人的时间。

这还包括用于从内存中释放 MediaPlayer 的 stopPlayer() 函数。这是一个很好的做法。

// Set to the volume of the MediaPlayer
float volume = 1;

private void startFadeOut(){

    // The duration of the fade
    final int FADE_DURATION = 3000;

    // The amount of time between volume changes. The smaller this is, the smoother the fade
    final int FADE_INTERVAL = 250;

    // Calculate the number of fade steps
    int numberOfSteps = FADE_DURATION / FADE_INTERVAL;

    // Calculate by how much the volume changes each step
    final float deltaVolume = volume / numberOfSteps;

    // Create a new Timer and Timer task to run the fading outside the main UI thread
    final Timer timer = new Timer(true);
    TimerTask timerTask = new TimerTask() {
        @Override
        public void run() {

            //Do a fade step
            fadeOutStep(deltaVolume);

            //Cancel and Purge the Timer if the desired volume has been reached
            if(volume <= 0){
                timer.cancel();
                timer.purge();
                stopPlayer();
            }
        }
    };

    timer.schedule(timerTask,FADE_INTERVAL,FADE_INTERVAL);
}

private void fadeOutStep(float deltaVolume){
    player.setVolume(volume, volume);
    volume -= deltaVolume;
}

// Release the player from memory
private void stopPlayer() {

    if (player != null) {

        player.release();
        player = null;
    }
}

Answer 3

在 API 级别 26 (https://developer.android.com/guide/topics/media/volumeshaper) 中添加了 VolumeShaper class。这是音量输出和输入的示例，您可以调整淡入或淡出速度（斜坡），向时间和音量数组添加更多点。时间点必须从 0 开始到 1 结束，它们是音量上升的相对时间。

fun fadeOutConfig(duration: Long): VolumeShaper.Configuration {
        val times = floatArrayOf(0f, 1f) // can add more points, volume points must correspond to time points
        val volumes = floatArrayOf(1f, 0f)
        return VolumeShaper.Configuration.Builder()
            .setDuration(duration)
            .setCurve(times, volumes)
            .setInterpolatorType(VolumeShaper.Configuration.INTERPOLATOR_TYPE_CUBIC)
            .build()
    }

fun fadeInConfig(duration: Long): VolumeShaper.Configuration {
    val times = floatArrayOf(0f, 1f) // can add more points, volume points must correspond to time points
    val volumes = floatArrayOf(0f, 1f)
    return VolumeShaper.Configuration.Builder()
        .setDuration(duration)
        .setCurve(times, volumes)
            .setInterpolatorType(VolumeShaper.Configuration.INTERPOLATOR_TYPE_CUBIC)
            .build()
}

fun fadeInOrOutAudio(mediaPlayer: MediaPlayer, duration: Long, out: Boolean) {
    val config = if (out) fadeOutConfig(duration) else fadeInConfig(duration)
    val volumeShaper = mediaPlayer.createVolumeShaper(config)
    volumeShaper.apply(VolumeShaper.Operation.PLAY)
}

Answer 4

private void fadeOut() {

    final long steps = 30;
    final double stepWidth = (double) 1 / steps;

    mFadeOutCriteria = 1;

    handler.postDelayed(new Runnable() {
        @Override
        public void run() {
            mFadeOutCriteria -= stepWidth;
            mediaPlayer.setVolume(mFadeOutCriteria, mFadeOutCriteria);

            if (mFadeOutCriteria <= 0) {
                mediaPlayer.stop();
                nextrunq();
                mFadeOutCriteria = 0;
                handler.removeCallbacks(this);
            } else
                handler.postDelayed(this, 100);
        }
    }, 100);
}

Android Studio Mediaplayer如何淡入淡出

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