Android Audio代码分析17 - setvolume函数

下面来看看音量设置相关的接口。

*****************************************源码*************************************************

//Test case 1: setStereoVolume() with max volume returns SUCCESS
@LargeTest
public void testSetStereoVolumeMax() throws Exception {
// constants for test
final String TEST_NAME = "testSetStereoVolumeMax";
final int TEST_SR = 22050;
final int TEST_CONF = AudioFormat.CHANNEL_OUT_STEREO;
final int TEST_FORMAT = AudioFormat.ENCODING_PCM_16BIT;
final int TEST_MODE = AudioTrack.MODE_STREAM;
final int TEST_STREAM_TYPE = AudioManager.STREAM_MUSIC;

//-------- initialization --------------
int minBuffSize = AudioTrack.getMinBufferSize(TEST_SR, TEST_CONF, TEST_FORMAT);
AudioTrack track = new AudioTrack(TEST_STREAM_TYPE, TEST_SR, TEST_CONF, TEST_FORMAT,
minBuffSize, TEST_MODE);
byte data[] = new byte[minBuffSize/2];
//--------    test        --------------
track.write(data, 0, data.length);
track.write(data, 0, data.length);
track.play();
float maxVol = AudioTrack.getMaxVolume();
assertTrue(TEST_NAME, track.setStereoVolume(maxVol, maxVol) == AudioTrack.SUCCESS);
//-------- tear down      --------------
track.release();
}

**********************************************************************************************

源码路径：

frameworks\base\media\tests\mediaframeworktest\src\com\android\mediaframeworktest\functional\MediaAudioTrackTest.java

#######################说明################################

//Test case 1: setStereoVolume() with max volume returns SUCCESS
@LargeTest
public void testSetStereoVolumeMax() throws Exception {
// constants for test
final String TEST_NAME = "testSetStereoVolumeMax";
final int TEST_SR = 22050;
final int TEST_CONF = AudioFormat.CHANNEL_OUT_STEREO;
final int TEST_FORMAT = AudioFormat.ENCODING_PCM_16BIT;
final int TEST_MODE = AudioTrack.MODE_STREAM;
final int TEST_STREAM_TYPE = AudioManager.STREAM_MUSIC;

//-------- initialization --------------
int minBuffSize = AudioTrack.getMinBufferSize(TEST_SR, TEST_CONF, TEST_FORMAT);
AudioTrack track = new AudioTrack(TEST_STREAM_TYPE, TEST_SR, TEST_CONF, TEST_FORMAT,
minBuffSize, TEST_MODE);
byte data[] = new byte[minBuffSize/2];
//--------    test        --------------
track.write(data, 0, data.length);
track.write(data, 0, data.length);
track.play();
float maxVol = AudioTrack.getMaxVolume();
// ++++++++++++++++++++++++++++++getMaxVolume++++++++++++++++++++++++++++++++++
/**
* Returns the maximum valid volume value. Volume values set above this one will
* be clamped at this value.
* @return the maximum volume expressed as a linear attenuation.
*/
static public float getMaxVolume() {
return AudioTrack.VOLUME_MAX;
}
// ------------------------------getMaxVolume----------------------------------
assertTrue(TEST_NAME, track.setStereoVolume(maxVol, maxVol) == AudioTrack.SUCCESS);
// ++++++++++++++++++++++++++++++setStereoVolume++++++++++++++++++++++++++++++++++
/**
* Sets the specified left/right output volume values on the AudioTrack. Values are clamped
* to the ({@link #getMinVolume()}, {@link #getMaxVolume()}) interval if outside this range.
* @param leftVolume output attenuation for the left channel. A value of 0.0f is silence,
*      a value of 1.0f is no attenuation.
* @param rightVolume output attenuation for the right channel
* @return error code or success, see {@link #SUCCESS},
*    {@link #ERROR_INVALID_OPERATION}
*/
public int setStereoVolume(float leftVolume, float rightVolume) {
if (mState != STATE_INITIALIZED) {
return ERROR_INVALID_OPERATION;
}

// 确保音量在[min, max]范围之内。
// clamp the volumes
if (leftVolume < getMinVolume()) {
leftVolume = getMinVolume();
}
if (leftVolume > getMaxVolume()) {
leftVolume = getMaxVolume();
}
if (rightVolume < getMinVolume()) {
rightVolume = getMinVolume();
}
if (rightVolume > getMaxVolume()) {
rightVolume = getMaxVolume();
}

native_setVolume(leftVolume, rightVolume);
// ++++++++++++++++++++++++++++android_media_AudioTrack_set_volume++++++++++++++++++++++++++++++++++++
static void
android_media_AudioTrack_set_volume(JNIEnv *env, jobject thiz, jfloat leftVol, jfloat rightVol )
{
AudioTrack *lpTrack = (AudioTrack *)env->GetIntField(
thiz, javaAudioTrackFields.nativeTrackInJavaObj);
if (lpTrack == NULL ) {
jniThrowException(env, "java/lang/IllegalStateException",
"Unable to retrieve AudioTrack pointer for setVolume()");
return;
}

lpTrack->setVolume(leftVol, rightVol);
// +++++++++++++++++++++++++++++AudioTrack::setVolume++++++++++++++++++++++++++++++++++
status_t AudioTrack::setVolume(float left, float right)
{
// 范围检查
if (left > 1.0f || right > 1.0f) {
return BAD_VALUE;
}

// 将音量保存到成员变量中
// 函数AudioTrack::set中会将这两个音量初始化为1.0f
// 函数AudioTrack::getVolume会取出这两个音量值
// 函数AudioTrack::createTrack中会将这两个值赋值给mCblk->volumeLR
mVolume[LEFT] = left;
mVolume[RIGHT] = right;

// write must be atomic
// 从audio_track_cblk_t的定义可知，volume的信息其实是一个union，这儿是作为volumeLR存入的，
// 用的时候其实是作为uint16_t    volume[2]数组来使用的。
// +++++++++++++++++++++++++++++union+++++++++++++++++++++++++++++++++++
volatile    union {
uint16_t    volume[2];
uint32_t    volumeLR;
};
// -----------------------------union-----------------------------------
// 类AudioMixer中，将数据从audio_track_cblk_t copy 到main buffer时，会根据音量对数据进行处理。
// 如以前我们看过的process__OneTrack16BitsStereoNoResampling函数。
mCblk->volumeLR = (uint32_t(uint16_t(right * 0x1000)) << 16) | uint16_t(left * 0x1000);

return NO_ERROR;
}
// -----------------------------AudioTrack::setVolume----------------------------------
}
// ----------------------------android_media_AudioTrack_set_volume------------------------------------

return SUCCESS;
}
// ------------------------------setStereoVolume----------------------------------
//-------- tear down      --------------
track.release();
}

###########################################################

&&&&&&&&&&&&&&&&&&&&&&&总结&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&

函数setStereoVolume最终设置的是软音量。

类AudioMixer中将数据从audio_track_cblk_t copy 到main buffer时，会使用音量对数据进行处理。

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