Android ToneGenerator startTone() 在第一次调用时非常慢

Question

我反复拨打ToneGenerator.startTone() 以发出短促的声音。但是在第一次调用时，它会阻塞很长时间。所以第一次爆发太长了。这是一个例子：

成员变量：

private ToneGenerator mDTMFPlayer

在构造函数中：

mDTMFPlayer = new ToneGenerator(AudioManager.STREAM_VOICE_CALL, TONE_RELATIVE_VOLUME);

在OnClickListener.onClick() 发起的Thread 中：

long startTime = System.currentTimeMillis();
mDTMFPlayer.startTone(ToneGenerator.TONE_DTMF_0);
Log.d(TAG,"After 1st: " + (System.currentTimeMillis() - startTime));
try { Thread.sleep(160); } catch (InterruptedException e) { }
mDTMFPlayer.stopTone();

startTime = System.currentTimeMillis();
mDTMFPlayer.startTone(ToneGenerator.TONE_DTMF_0);
Log.d(TAG,"After 2nd: " + (System.currentTimeMillis() - startTime));
try { Thread.sleep(160); } catch (InterruptedException e) { }
mDTMFPlayer.stopTone();

startTime = System.currentTimeMillis();
mDTMFPlayer.startTone(ToneGenerator.TONE_DTMF_0);
Log.d(TAG,"After 3rd: " + (System.currentTimeMillis() - startTime));
try { Thread.sleep(160); } catch (InterruptedException e) { }
mDTMFPlayer.stopTone();

这是输出，执行时间为startTone()，以毫秒为单位：

11-16 18:07:35.885 16927-17977/com.my.project D/Ring: After 1st: 454
11-16 18:07:36.502 16927-17977/com.my.project D/Ring: After 2nd: 0
11-16 18:07:36.672 16927-17977/com.my.project D/Ring: After 3rd: 1

第一个电话阻塞了将近半秒，这对于我的需要来说太长了。之后的任何调用都会使阻塞消失一段时间。奇怪的是，如果我稍等片刻再试一次，它又变慢了。似乎有一段时间后阻塞又回来了。

请指教。

Answer 1

我认为是 AudioManager.STREAM_VOICE_CALL 造成的。我设计的行为与您的相似。在我运行应用程序后，第一个 startTone() 调用的初始化时间很长。如果我退出并进入应用程序，所有 3 个呼叫都可以很快。但是如果在应用启动之前播放一些系统声音，它会显示相同的“慢，快，快”结果。

所以我想它与流切换/阻塞有关，因为使用AudioManager.STREAM_NOTIFICATION 在我的设备上只需要 4-10 毫秒。也可以在这里阅读更多信息：What is the difference between AudioManager's stream types at low level?

考虑这段代码：

for (int i = -1; i < 10; i++) {
    System.out.println("AudioSystem stream " + i);
    mDTMFPlayer = new ToneGenerator(i, TONE_RELATIVE_VOLUME);
    long startTime = System.currentTimeMillis();
    mDTMFPlayer.startTone(ToneGenerator.TONE_DTMF_0);
    Log.d(TAG, "After 1st: " + (System.currentTimeMillis() - startTime));
    try {Thread.sleep(160);} catch (InterruptedException e) {}
    mDTMFPlayer.stopTone();

    startTime = System.currentTimeMillis();
    mDTMFPlayer.startTone(ToneGenerator.TONE_DTMF_0);
    Log.d(TAG, "After 2nd: " + (System.currentTimeMillis() - startTime));
    try {Thread.sleep(160);} catch (InterruptedException e) {}
    mDTMFPlayer.stopTone();

    startTime = System.currentTimeMillis();
    mDTMFPlayer.startTone(ToneGenerator.TONE_DTMF_0);
    Log.d(TAG, "After 3rd: " + (System.currentTimeMillis() - startTime));
    try {Thread.sleep(160);} catch (InterruptedException e) {}
    mDTMFPlayer.stopTone();
    mDTMFPlayer.release();
}

输出：

I/System.out: AudioSystem stream -1 STREAM_DEFAULT
D/com.example.MainActivity: After 1st: 8
D/com.example.MainActivity: After 2nd: 1
D/com.example.MainActivity: After 3rd: 1
I/System.out: AudioSystem stream 0 STREAM_VOICE_CALL
D/com.example.MainActivity: After 1st: 325
D/com.example.MainActivity: After 2nd: 1
D/com.example.MainActivity: After 3rd: 1
I/System.out: AudioSystem stream 1 STREAM_SYSTEM
D/com.example.MainActivity: After 1st: 17
D/com.example.MainActivity: After 2nd: 2
D/com.example.MainActivity: After 3rd: 3
I/System.out: AudioSystem stream 2 STREAM_RING
D/com.example.MainActivity: After 1st: 28
D/com.example.MainActivity: After 2nd: 2
D/com.example.MainActivity: After 3rd: 1
I/System.out: AudioSystem stream 3 STREAM_MUSIC
D/com.example.MainActivity: After 1st: 19
D/com.example.MainActivity: After 2nd: 1
D/com.example.MainActivity: After 3rd: 1
I/System.out: AudioSystem stream 4 STREAM_ALARM
D/com.example.MainActivity: After 1st: 28
D/com.example.MainActivity: After 2nd: 1
D/com.example.MainActivity: After 3rd: 1
I/System.out: AudioSystem stream 5 STREAM_NOTIFICATION
D/com.example.MainActivity: After 1st: 16
D/com.example.MainActivity: After 2nd: 1
D/com.example.MainActivity: After 3rd: 1
I/System.out: AudioSystem stream 6 STREAM_BLUETOOTH_SCO
D/com.example.MainActivity: After 1st: 332
D/com.example.MainActivity: After 2nd: 2
D/com.example.MainActivity: After 3rd: 1
I/System.out: AudioSystem stream 7 STREAM_SYSTEM_ENFORCED
D/com.example.MainActivity: After 1st: 324
D/com.example.MainActivity: After 2nd: 1
D/com.example.MainActivity: After 3rd: 1
I/System.out: AudioSystem stream 8 STREAM_DTMF
D/com.example.MainActivity: After 1st: 26
D/com.example.MainActivity: After 2nd: 2
D/com.example.MainActivity: After 3rd: 4
I/System.out: AudioSystem stream 9 STREAM_TTS
D/com.example.MainActivity: After 1st: 12
D/com.example.MainActivity: After 2nd: 4
D/com.example.MainActivity: After 3rd: 2  

顺便说一句，如果你想研究相关的C源代码你可以看看android_media_ToneGenerator.cpp，ToneGenerator.h，ToneGenerator.cppAudioService.java