场景：使用AudioTrack播放一段音频，streamtype是AUDIO_STREAM_MUSIC；
跟踪音频输出设备选择的流程，代码会走到这里：
1.frameworks\av\media\libaudioclient\AudioTrack.cpp
status_t AudioTrack::createTrack_l(){
......
//假设此时播放的是音乐，那这里的streamType是Music类型，所以属性attr为NULL
audio_attributes_t *attr = (mStreamType == AUDIO_STREAM_DEFAULT) ? &mAttributes : NULL;
......
//通过属性以及stream的类型获取当前track输出的output设备；
//传入的audio_attributes_t等参数，带回output
status = AudioSystem::getOutputForAttr(attr, &output,
mSessionId, &streamType, mClientUid,
&config,
mFlags, &mRoutedDeviceId, &mPortId);
......
}
2.frameworks\av\media\libaudioclient\AudioSystem.cpp
status_t AudioSystem::getOutputForAttr(const audio_attributes_t *attr,
audio_io_handle_t *output,
audio_session_t session,
audio_stream_type_t *stream,
uid_t uid,
const audio_config_t *config,
audio_output_flags_t flags,
audio_port_handle_t *selectedDeviceId,
audio_port_handle_t *portId)
{
//实现类是AudioPolicyInterfaceImpl
const sp<IAudioPolicyService>& aps = AudioSystem::get_audio_policy_service();
if (aps == 0) return NO_INIT;
//调用AudioPolicyInterfaceImpl.getOutputForAttr();
return aps->getOutputForAttr(attr, output, session, stream, uid,
config,
flags, selectedDeviceId, portId);
}
3.frameworks\av\services\audiopolicy\service\AudioPolicyInterfaceImpl.cpp
status_t AudioPolicyService::getOutputForAttr(const audio_attributes_t *attr,
audio_io_handle_t *output,
audio_session_t session,
audio_stream_type_t *stream,
uid_t uid,
const audio_config_t *config,
audio_output_flags_t flags,
audio_port_handle_t *selectedDeviceId,
audio_port_handle_t *portId)
{
if (mAudioPolicyManager == NULL) {
return NO_INIT;
}
ALOGV("getOutput()");
Mutex::Autolock _l(mLock);
const uid_t callingUid = IPCThreadState::self()->getCallingUid();
if (!isTrustedCallingUid(callingUid) || uid == (uid_t)-1) {
ALOGW_IF(uid != (uid_t)-1 && uid != callingUid,
"%s uid %d tried to pass itself off as %d", __FUNCTION__, callingUid, uid);
uid = callingUid;
}
//进入AudioPolicyManager
return mAudioPolicyManager->getOutputForAttr(attr, output, session, stream, uid,
config,
flags, selectedDeviceId, portId);
}
4.frameworks\av\services\audiopolicy\managerdefault\AudioPolicyManager.cpp
status_t AudioPolicyManager::getOutputForAttr(const audio_attributes_t *attr,
audio_io_handle_t *output,
audio_session_t session,
audio_stream_type_t *stream,
uid_t uid,
const audio_config_t *config,
audio_output_flags_t flags,
audio_port_handle_t *selectedDeviceId,
audio_port_handle_t *portId)
{
audio_attributes_t attributes;
//对于当前music的track，传入的attr是NULL,
if (attr != NULL) {//判断不走
if (!isValidAttributes(attr)) {
ALOGE("getOutputForAttr() invalid attributes: usage=%d content=%d flags=0x%x tags=[%s]",
attr->usage, attr->content_type, attr->flags,
attr->tags);
return BAD_VALUE;
}
attributes = *attr;
} else {
if (*stream < AUDIO_STREAM_MIN || *stream >= AUDIO_STREAM_PUBLIC_CNT) {
ALOGE("getOutputForAttr(): invalid stream type");
return BAD_VALUE;
}
//①将stream保存到attributes的属性中
/*对于当前music的场景,attributes会被如下赋值
attr->content_type = AUDIO_CONTENT_TYPE_MUSIC;
attr->usage = AUDIO_USAGE_MEDIA;
*/
stream_type_to_audio_attributes(*stream, &attributes);
}
......
*stream = streamTypefromAttributesInt(&attributes);
......
//②根据当前音频的属性，获取当前track的音频策略，根据attributes选中Strategy
routing_strategy strategy = (routing_strategy) getStrategyForAttr(&attributes);
//③根据当前track的音频策略，获取当前音频的输出终端，根据Strategy选中device
audio_devices_t device = getDeviceForStrategy(strategy, false /*fromCache*/);
if ((attributes.flags & AUDIO_FLAG_HW_AV_SYNC) != 0) {
flags = (audio_output_flags_t)(flags | AUDIO_OUTPUT_FLAG_HW_AV_SYNC);
}
ALOGV("getOutputForAttr() device 0x%x, samplingRate %d, format %x, channelMask %x, flags %x",
device, config->sample_rate, config->format, config->channel_mask, flags);
//④根据音频设备，音频输出标识，format等选择输出路径，根据选定的device获取Output
*output = getOutputForDevice(device, session, *stream,
config->sample_rate, config->format, config->channel_mask,
flags, &config->offload_info);
......
return NO_ERROR;
}
先看①：stream_type_to_audio_attributes(*stream, &attributes)，将stream保存到attributes的属性中：
frameworks\av\media\libaudioclient\include\media\AudioPolicyHelper.h
static inline
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);
}
}
content_type:具体输出类型。android当前一共提供了11种stream_type,但一旦进入到Attribute，Android就只将其整理成几种类型。这才是实际的类型。
这里的stream_type，usage定义在audio-base.h中，content_type定义在了audio.h中：
1.system\media\audio\include\system\audio-base.h
typedef enum {
AUDIO_STREAM_DEFAULT = -1, // (-1)
AUDIO_STREAM_MIN = 0,
AUDIO_STREAM_VOICE_CALL = 0,
AUDIO_STREAM_SYSTEM = 1,
AUDIO_STREAM_RING = 2,
AUDIO_STREAM_MUSIC = 3,
AUDIO_STREAM_ALARM = 4,
AUDIO_STREAM_NOTIFICATION = 5,
AUDIO_STREAM_BLUETOOTH_SCO = 6,
AUDIO_STREAM_ENFORCED_AUDIBLE = 7,
AUDIO_STREAM_DTMF = 8,
AUDIO_STREAM_TTS = 9,
AUDIO_STREAM_ACCESSIBILITY = 10,
AUDIO_STREAM_REROUTING = 11,
AUDIO_STREAM_PATCH = 12,
AUDIO_STREAM_PUBLIC_CNT = 11, // (ACCESSIBILITY + 1)
AUDIO_STREAM_FOR_POLICY_CNT = 12, // PATCH
AUDIO_STREAM_CNT = 13, // (PATCH + 1)
} audio_stream_type_t;
typedef enum {
AUDIO_USAGE_UNKNOWN = 0,
AUDIO_USAGE_MEDIA = 1,
AUDIO_USAGE_VOICE_COMMUNICATION = 2,
AUDIO_USAGE_VOICE_COMMUNICATION_SIGNALLING = 3,
AUDIO_USAGE_ALARM = 4,
AUDIO_USAGE_NOTIFICATION = 5,
AUDIO_USAGE_NOTIFICATION_TELEPHONY_RINGTONE = 6,
AUDIO_USAGE_NOTIFICATION_COMMUNICATION_REQUEST = 7,
AUDIO_USAGE_NOTIFICATION_COMMUNICATION_INSTANT = 8,
AUDIO_USAGE_NOTIFICATION_COMMUNICATION_DELAYED = 9,
AUDIO_USAGE_NOTIFICATION_EVENT = 10,
AUDIO_USAGE_ASSISTANCE_ACCESSIBILITY = 11,
AUDIO_USAGE_ASSISTANCE_NAVIGATION_GUIDANCE = 12,
AUDIO_USAGE_ASSISTANCE_SONIFICATION = 13,
AUDIO_USAGE_GAME = 14,
AUDIO_USAGE_VIRTUAL_SOURCE = 15,
AUDIO_USAGE_ASSISTANT = 16,
AUDIO_USAGE_CNT = 17,
AUDIO_USAGE_MAX = 16, // (CNT - 1)
} audio_usage_t;
2.system\media\audio\include\system\audio.h
typedef enum {
AUDIO_CONTENT_TYPE_UNKNOWN = 0,
AUDIO_CONTENT_TYPE_SPEECH = 1,
AUDIO_CONTENT_TYPE_MUSIC = 2,
AUDIO_CONTENT_TYPE_MOVIE = 3,
AUDIO_CONTENT_TYPE_SONIFICATION = 4,
AUDIO_CONTENT_TYPE_CNT,
AUDIO_CONTENT_TYPE_MAX = AUDIO_CONTENT_TYPE_CNT - 1,
} audio_content_type_t;
再看②： routing_strategy strategy = (routing_strategy) getStrategyForAttr(&attributes);//根据当前音频的属性，获取当前track的音频策略也就是根据attributes选中Strategy：
uint32_t AudioPolicyManager::getStrategyForAttr(const audio_attributes_t *attr) {
// flags to strategy mapping
if ((attr->flags & AUDIO_FLAG_BEACON) == AUDIO_FLAG_BEACON) {
return (uint32_t) STRATEGY_TRANSMITTED_THROUGH_SPEAKER;
}
if ((attr->flags & AUDIO_FLAG_AUDIBILITY_ENFORCED) == AUDIO_FLAG_AUDIBILITY_ENFORCED) {
return (uint32_t) STRATEGY_ENFORCED_AUDIBLE;
}
// usage to strategy mapping
//进入Engine.cpp
//这里范围音频策略是：STRATEGY_MEDIA
return static_cast<uint32_t>(mEngine->getStrategyForUsage(attr->usage));
}
frameworks\av\services\audiopolicy\enginedefault\src\Engine.cpp
routing_strategy Engine::getStrategyForUsage(audio_usage_t usage)
{
// usage to strategy mapping
switch (usage) {
case AUDIO_USAGE_ASSISTANCE_ACCESSIBILITY:
return STRATEGY_ACCESSIBILITY;
case AUDIO_USAGE_MEDIA:
case AUDIO_USAGE_GAME:
case AUDIO_USAGE_ASSISTANT:
case AUDIO_USAGE_ASSISTANCE_NAVIGATION_GUIDANCE:
case AUDIO_USAGE_ASSISTANCE_SONIFICATION:
return STRATEGY_MEDIA;
case AUDIO_USAGE_VOICE_COMMUNICATION:
return STRATEGY_PHONE;
case AUDIO_USAGE_VOICE_COMMUNICATION_SIGNALLING:
return STRATEGY_DTMF;
case AUDIO_USAGE_ALARM:
case AUDIO_USAGE_NOTIFICATION_TELEPHONY_RINGTONE:
return STRATEGY_SONIFICATION;
case AUDIO_USAGE_NOTIFICATION:
case AUDIO_USAGE_NOTIFICATION_COMMUNICATION_REQUEST:
case AUDIO_USAGE_NOTIFICATION_COMMUNICATION_INSTANT:
case AUDIO_USAGE_NOTIFICATION_COMMUNICATION_DELAYED:
case AUDIO_USAGE_NOTIFICATION_EVENT:
return STRATEGY_SONIFICATION_RESPECTFUL;
case AUDIO_USAGE_UNKNOWN:
default:
return STRATEGY_MEDIA;
}
}
音频策略strategy定义在RoutingStrategy.h中：
frameworks\av\services\audiopolicy\common\include\RoutingStrategy.h
enum routing_strategy {
STRATEGY_MEDIA,
STRATEGY_PHONE,
STRATEGY_SONIFICATION,
STRATEGY_SONIFICATION_RESPECTFUL,
STRATEGY_DTMF,
STRATEGY_ENFORCED_AUDIBLE,
STRATEGY_TRANSMITTED_THROUGH_SPEAKER,
STRATEGY_ACCESSIBILITY,
STRATEGY_REROUTING,
NUM_STRATEGIES
};
然后看③： audio_devices_t device = getDeviceForStrategy(strategy, false /*fromCache*/);//根据当前track的音频策略，获取当前音频的输出终端，也就是根据Strategy选中device：
audio_devices_t AudioPolicyManager::getDeviceForStrategy(routing_strategy strategy,
bool fromCache)
{
......
return mEngine->getDeviceForStrategy(strategy);
}
frameworks\av\services\audiopolicy\enginedefault\src\Engine.cpp
audio_devices_t Engine::getDeviceForStrategy(routing_strategy strategy) const
{
DeviceVector availableOutputDevices = mApmObserver->getAvailableOutputDevices();
DeviceVector availableInputDevices = mApmObserver->getAvailableInputDevices();
const SwAudioOutputCollection &outputs = mApmObserver->getOutputs();
return getDeviceForStrategyInt(strategy, availableOutputDevices,
availableInputDevices, outputs);
}
策略，USAGE，STREAM对应关系如下：
STRATEGY_ACCESSIBILITY
AUDIO_USAGE_ASSISTANCE_ACCESSIBILITY // 11
AUDIO_STREAM_TTS // 9
STRATEGY_MEDIA
AUDIO_USAGE_MEDIA // 1
AUDIO_STREAM_DEFAULT // -1
AUDIO_STREAM_MUSIC // 3
AUDIO_USAGE_GAME
AUDIO_USAGE_ASSISTANT
AUDIO_USAGE_ASSISTANCE_NAVIGATION_GUIDANCE
AUDIO_USAGE_ASSISTANCE_SONIFICATION // 11
AUDIO_STREAM_ENFORCED_AUDIBLE // 7
AUDIO_STREAM_SYSTEM // 1
STRATEGY_PHONE
AUDIO_USAGE_VOICE_COMMUNICATION // 2
AUDIO_STREAM_VOICE_CALL // 0
AUDIO_STREAM_BLUETOOTH_SCO // 6
STRATEGY_DTMF
AUDIO_USAGE_VOICE_COMMUNICATION_SIGNALLING // 3
AUDIO_STREAM_DTMF // 8
STRATEGY_SONIFICATION
AUDIO_USAGE_ALARM // 4
AUDIO_STREAM_ALARM // 4
AUDIO_USAGE_NOTIFICATION_TELEPHONY_RINGTONE // 6
AUDIO_STREAM_RING // 2
STRATEGY_SONIFICATION_RESPECTFUL
AUDIO_USAGE_NOTIFICATION // 5
AUDIO_STREAM_NOTIFICATION // 5
AUDIO_USAGE_NOTIFICATION_COMMUNICATION_REQUEST
AUDIO_USAGE_NOTIFICATION_COMMUNICATION_INSTANT
AUDIO_USAGE_NOTIFICATION_COMMUNICATION_DELAYED
AUDIO_USAGE_NOTIFICATION_EVENT
STRATEGY_MEDIA
AUDIO_USAGE_UNKNOWN // 0
default
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