Android Camera 拍照/攝像提示音

     其實，Camera 拍照/攝像提示音是爲了防止偷拍，業內有不成文規定，手機公司在作camera時，點擊拍照和錄像鍵的時候，必需要有提示音。所以，google也就很是人性化的將播放拍照聲音的函數，放到了cameraService中，防止開發者能開發出不響的camera，從而只要調用拍照函數，必定會響，這是寫死在framework中的。

Camera真正播放提示音的是在CameraService.cpp中的playSound()方法，這個方法提供給拍照/攝像時調用。

// /frameworks/base/services/camera/libcameraservice/CameraService.cpp
void CameraService::playSound(sound_kind kind) {
    LOG1("playSound(%d)", kind);
    Mutex::Autolock lock(mSoundLock);
    sp<MediaPlayer> player = mSoundPlayer[kind];
    if (player != 0) {
        player->seekTo(0);
        player->start();
    }
}

下面就是在開始攝像時會調用playSound()方法播放提示音：

status_t CameraService::Client::startRecordingMode() {
    LOG1("startRecordingMode");
    status_t result = NO_ERROR;

    // if recording has been enabled, nothing needs to be done
    if (mHardware->recordingEnabled()) {
        return NO_ERROR;
    }
    // if preview has not been started, start preview first
    if (!mHardware->previewEnabled()) {
        result = startPreviewMode();
        if (result != NO_ERROR) {
            return result;
        }
    }
    // start recording mode
    enableMsgType(CAMERA_MSG_VIDEO_FRAME);
    mCameraService->playSound(SOUND_RECORDING);
    result = mHardware->startRecording();
    if (result != NO_ERROR) {
        LOGE("mHardware->startRecording() failed with status %d", result);
    }
    return result;
}

有時，攝像的同時會將這個提示音也錄入，要解決這個問題，能夠在mCameraService->playSOund(SOUND_RECORDING)後加一個延時，但這個延時不能用sleep()方法（會報一些莫名其妙的問題，直接就stopReCording），能夠用usleep()實現延時。

原文參考：http://blog.csdn.net/dyfleoo/article/details/7912021