Android Audio程式碼分析17 – setvolume函數

下面來看看音量設定相關的介面。

*****************************************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();    }

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源碼路徑：
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;        }// 確保音量在[min, max]範圍之內。        // 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 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){// 範圍檢查    if (left > 1.0f || right > 1.0f) {        return BAD_VALUE;    }// 將音量儲存到成員變數中// 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的資訊其實是一個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，將資料從audio_track_cblk_t copy 到main buffer時，會根據音量對資料進行處理。// 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();    }

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函數setStereoVolume最終設定的是軟音量。
類AudioMixer中將資料從audio_track_cblk_t copy 到main buffer時，會使用音量對資料進行處理。
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