Android Audio代码分析17 - setvolume函数 - android

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();    }

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源码路径：
frameworks\base\media\tests\mediaframeworktest\src\com\android\mediaframeworktest\functional\MediaAudioTrackTest.java

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    //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 voidandroid_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();    }

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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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Android Audio代码分析17 - setvolume函数

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