Audio播放流程(三)---MediaPlayerService流程之setAudioStreamType以及prepare

1.setAudioStreamType的过程

frameworks\av\media\libmediaplayerservice\MediaPlayerService.cpp

status_t MediaPlayerService::Client::setAudioStreamType(audio_stream_type_t type)
{
    ALOGE("[%d] setAudioStreamType(%d)", mConnId, type);
    // TODO: for hardware output, call player instead
    Mutex::Autolock l(mLock);
    if (mAudioOutput != 0) mAudioOutput->setAudioStreamType(type);
    return NO_ERROR;
}

这里的mAudioOutput是在Audio播放流程(二)—MediaPlayerService流程之setDataSource中创建的。

setDataSource_pre
	mAudioOutput = new AudioOutput(...)
	将AudioOutput设置为NuPlayer的Sink端
	static_cast<MediaPlayerInterface*>(p.get())->setAudioSink(mAudioOutput);

继续

void MediaPlayerService::AudioOutput::setAudioStreamType(audio_stream_type_t streamType)
{
    Mutex::Autolock lock(mLock);
    // do not allow direct stream type modification if attributes have been set
    if (mAttributes == NULL) {
        mStreamType = streamType;
        // No attributes are set, for mediaPlayer playback, force populate attributes
        // This is done to ensure that we qualify for a direct output
        mAttributes = (audio_attributes_t *) calloc(1, sizeof(audio_attributes_t));
        if (mAttributes != NULL) {
            stream_type_to_audio_attributes(mStreamType, mAttributes);
        }
    }
}
...
static void stream_type_to_audio_attributes(audio_stream_type_t streamType,
                                     audio_attributes_t *attr) {
    memset(attr, 0, sizeof(audio_attributes_t));

    switch (streamType) {
    case AUDIO_STREAM_DEFAULT:
    case AUDIO_STREAM_MUSIC:
        attr->content_type = AUDIO_CONTENT_TYPE_MUSIC;
        attr->usage = AUDIO_USAGE_MEDIA;
        break;
    case AUDIO_STREAM_VOICE_CALL:
        attr->content_type = AUDIO_CONTENT_TYPE_SPEECH;
        attr->usage = AUDIO_USAGE_VOICE_COMMUNICATION;
        break;
    case AUDIO_STREAM_ENFORCED_AUDIBLE:
        attr->flags  |= AUDIO_FLAG_AUDIBILITY_ENFORCED;
        // intended fall through, attributes in common with STREAM_SYSTEM
    case AUDIO_STREAM_SYSTEM:
        attr->content_type = AUDIO_CONTENT_TYPE_SONIFICATION;
        attr->usage = AUDIO_USAGE_ASSISTANCE_SONIFICATION;
        break;
    case AUDIO_STREAM_RING:
        attr->content_type = AUDIO_CONTENT_TYPE_SONIFICATION;
        attr->usage = AUDIO_USAGE_NOTIFICATION_TELEPHONY_RINGTONE;
        break;
    case AUDIO_STREAM_ALARM:
        attr->content_type = AUDIO_CONTENT_TYPE_SONIFICATION;
        attr->usage = AUDIO_USAGE_ALARM;
        break;
    case AUDIO_STREAM_NOTIFICATION:
        attr->content_type = AUDIO_CONTENT_TYPE_SONIFICATION;
        attr->usage = AUDIO_USAGE_NOTIFICATION;
        break;
    case AUDIO_STREAM_BLUETOOTH_SCO:
        attr->content_type = AUDIO_CONTENT_TYPE_SPEECH;
        attr->usage = AUDIO_USAGE_VOICE_COMMUNICATION;
        attr->flags |= AUDIO_FLAG_SCO;
        break;
    case AUDIO_STREAM_DTMF:
        attr->content_type = AUDIO_CONTENT_TYPE_SONIFICATION;
        attr->usage = AUDIO_USAGE_VOICE_COMMUNICATION_SIGNALLING;
        break;
    case AUDIO_STREAM_TTS:
        attr->content_type = AUDIO_CONTENT_TYPE_SPEECH;
        attr->usage = AUDIO_USAGE_ASSISTANCE_ACCESSIBILITY;
        break;
    default:
        ALOGE("invalid stream type %d when converting to attributes", streamType);
    }
}                          

这个API还是很简单的，就是设置音频的属性，例如：

``case AUDIO_STREAM_MUSIC:
	attr->content_type = AUDIO_CONTENT_TYPE_MUSIC;
	attr->usage = AUDIO_USAGE_MEDIA;``