下面來看看音量設置相關的接口。
*****************************************源碼*************************************************
//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();
}
**********************************************************************************************
源碼路徑：
frameworks\base\media\tests\mediaframeworktest\src\com\android\mediaframeworktest\functional\MediaAudioTrackTest.java
#######################說明################################
//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;
}
// 確保音量在[min, max]范圍之內。
// 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)
{
// 范圍檢查
if (left > 1.0f || right > 1.0f) {
return BAD_VALUE;
}
// 將音量保存到成員變量中
// 函數AudioTrack::set中會將這兩個音量初始化為1.0f
// 函數AudioTrack::getVolume會取出這兩個音量值
// 函數AudioTrack::createTrack中會將這兩個值賦值給mCblk->volumeLR
mVolume[LEFT] = left;
mVolume[RIGHT] = right;
// write must be atomic
// 從audio_track_cblk_t的定義可知，volume的信息其實是一個union，這兒是作為volumeLR存入的，
// 用的時候其實是作為uint16_t volume[2]數組來使用的。
+++++++++++++++++++++++++++++union+++++++++++++++++++++++++++++++++++
volatile union {
uint16_t volume[2];
uint32_t volumeLR;
};
—————————–union———————————–
// 類AudioMixer中，將數據從audio_track_cblk_t copy 到main buffer時，會根據音量對數據進行處理。
// 如以前我們看過的process__OneTrack16BitsStereoNoResampling函數。
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();
}
###########################################################
&&&&&&&&&&&&&&&&&&&&&&&總結&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&
函數setStereoVolume最終設置的是軟音量。
類AudioMixer中將數據從audio_track_cblk_t copy 到main buffer時，會使用音量對數據進行處理。
&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&
摘自：江風的專欄
