Android(安卓)Audio代码分析19 - setPosition函数 - android

之前我们看过get position，今天来看看set position。

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

    //Test case 3: setPlaybackHeadPosition() on paused track    @LargeTest    public void testSetPlaybackHeadPositionPaused() throws Exception {        // constants for test        final String TEST_NAME = "testSetPlaybackHeadPositionPaused";        final int TEST_SR = 22050;        final int TEST_CONF = AudioFormat.CHANNEL_OUT_MONO;        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,                 2*minBuffSize, TEST_MODE);        byte data[] = new byte[minBuffSize];        //--------    test        --------------        assumeTrue(TEST_NAME, track.getState() == AudioTrack.STATE_INITIALIZED);        track.write(data, 0, data.length);        track.write(data, 0, data.length);        track.play();        track.pause();        assumeTrue(TEST_NAME, track.getPlayState() == AudioTrack.PLAYSTATE_PAUSED);        assertTrue(TEST_NAME, track.setPlaybackHeadPosition(10) == 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

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

    //Test case 3: setPlaybackHeadPosition() on paused track    @LargeTest    public void testSetPlaybackHeadPositionPaused() throws Exception {        // constants for test        final String TEST_NAME = "testSetPlaybackHeadPositionPaused";        final int TEST_SR = 22050;        final int TEST_CONF = AudioFormat.CHANNEL_OUT_MONO;        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,                 2*minBuffSize, TEST_MODE);        byte data[] = new byte[minBuffSize];        //--------    test        --------------        assumeTrue(TEST_NAME, track.getState() == AudioTrack.STATE_INITIALIZED);        track.write(data, 0, data.length);        track.write(data, 0, data.length);        track.play();        track.pause();        assumeTrue(TEST_NAME, track.getPlayState() == AudioTrack.PLAYSTATE_PAUSED);        assertTrue(TEST_NAME, track.setPlaybackHeadPosition(10) == AudioTrack.SUCCESS);// +++++++++++++++++++++++++++++setPlaybackHeadPosition+++++++++++++++++++++++++++++++++++    /**     * Sets the playback head position. The track must be stopped for the position to be changed.     * @param positionInFrames playback head position expressed in frames     * @return error code or success, see {@link #SUCCESS}, {@link #ERROR_BAD_VALUE},     *    {@link #ERROR_INVALID_OPERATION}     */    public int setPlaybackHeadPosition(int positionInFrames) {        synchronized(mPlayStateLock) {            if ((mPlayState == PLAYSTATE_STOPPED) || (mPlayState == PLAYSTATE_PAUSED)) {                return native_set_position(positionInFrames);// ++++++++++++++++++++++++++++android_media_AudioTrack_set_position++++++++++++++++++++++++++++++++++++static jint android_media_AudioTrack_set_position(JNIEnv *env,  jobject thiz,         jint position) {                AudioTrack *lpTrack = (AudioTrack *)env->GetIntField(                thiz, javaAudioTrackFields.nativeTrackInJavaObj);                    if (lpTrack) {        return android_media_translateErrorCode( lpTrack->setPosition(position) );// ++++++++++++++++++++++++++++AudioTrack::setPosition++++++++++++++++++++++++++++++++++++status_t AudioTrack::setPosition(uint32_t position){    Mutex::Autolock _l(mCblk->lock);    if (!stopped()) return INVALID_OPERATION;    if (position > mCblk->user) return BAD_VALUE;    mCblk->server = position;    mCblk->flags |= CBLK_FORCEREADY_ON;    return NO_ERROR;}// ----------------------------AudioTrack::setPosition------------------------------------    } else {        jniThrowException(env, "java/lang/IllegalStateException",            "Unable to retrieve AudioTrack pointer for setPosition()");        return AUDIOTRACK_ERROR;    }}// ----------------------------android_media_AudioTrack_set_position------------------------------------            } else {                return ERROR_INVALID_OPERATION;            }        }    }// -----------------------------setPlaybackHeadPosition-----------------------------------        //-------- tear down      --------------        track.release();    }

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set position改变的其实是audio_track_cblk_t结构体中的server成员。
也就是AudioMixer中从audio_track_cblk_t中copy数据时的起始地址。
这儿设置position有个限制，就是不能跑到user前面去，
即不能让取数据的其实地址超出已写数据的范围。
在播放器中，大幅度拖动进度条，改变的应该是读取文件时的地址，

而不是audio_track_cblk_t对象中的地址。

另外，只能在stop的状态下才能改变position。

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Android(安卓)Audio代码分析19 - setPosition函数

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