AIDL and HIDL Audio HAL comparison

Starting with Android 14, partners and SoC vendors are encouraged to replace the current HIDL HAL implementation with an AIDL HAL implementation.

To facilitate a smooth transition from HIDL Audio HAL to an AIDL Audio HAL, some of the key differences are highlighted on this page. This page also shows the mapping between the AIDL and HIDL interfaces for the Audio HAL.

Difference between AIDL and HIDL Audio HAL implementation

The main differences between the HIDL structure and the AIDL structure are as follows:

In AIDL Audio Core HAL, the IConfig interface is introduced as a replacement for the system-wide parameters in XML files in HIDL HAL. The framework reads these parameters from the Core HAL instead of the vendor configuration file. As an example, the list of surround formats that are surfaced for user control is provided by the IConfig.getSurroundSoundConfig method in the Core HAL.

In AIDL Audio Effects HAL, the effectProxy logic defined in XML files in HIDL Effects HAL is moved to the audio framework. The audio framework queries all effect instances in the system using IFactory.queryEffects, and all effect processings using IFactory.queryProcessing.
To avoid confusion with use of the term device for audio device types, IDevice in HIDL Audio HAL is renamed to IModule in the AIDL Audio HAL.
IPrimaryDevice is replaced in AIDL Audio HAL. Updates about the current audio mode and screen rotation are sent to every IModule instance. Parameters related to Bluetooth synchronous connection oriented (BT SCO) and Hands-Free Profile (HFP) are handled by a dedicated IBluetooth interface. A dedicated ITelephony interface provides telephony-specific controls. Instances of both of these interfaces can be retrieved from the primary instance of the IModule interface. See the comparison tables on Core HAL and Feature-related functionality for more information.
IDevicesFactory is removed in AIDL Audio HAL to avoid redundancy. HAL modules (that is, IModule interface instances) are now registered directly with the Service Manager using their names for instance names, such as, bluetooth or r_submix. The only exception is the primary module which registers under the instance name default.

AIDL and HIDL Audio HAL mapping

The tables in the following sections show the mapping between the HIDL and AIDL Audio HAL interfaces. See Audio HAL README file for more information on the directory structure.

Core HAL

All HIDL interfaces are within the android.hardware.audio@N.M package, where N.M denotes the Major.Minor version. All AIDL interfaces are within the android.hardware.audio.core package.

HIDL API interfaces and configuration files	AIDL API interfaces
`IDevicesFactory`	Registration of `IModule` with `ServiceManager`.
`IDevice`	`IModule`
`IPrimaryDevice`	`ITelephony` `IBluetooth`
`IStream` `IStreamIn` `IStreamOut`	`StreamDescriptor` `IStreamIn` `IStreamCommon` `IStreamOut`
`audio_policy_configuration.xml` `audio_policy_engine_configuration.xml`	`IConfig` `IModule`
Configurable Audio Policy files	Use the HIDL implementation for Android 14.

Audio ports, dynamic profiles, routes and patches

In this table, elements of XML files are designated using angle brackets.

HIDL API interface methods and configuration files elements	AIDL API interface methods
`<attachedDevices>` `<defaultOutputDevice>` `<mixPorts>` `<devicePorts>`	`IModule.getAudioPorts`
`IDevice.getAudioPort` `IDevice.setConnectedState`	`IModule.getAudioPort` `IModule.connectExternalDevice` `IModule.disconnectExternalDevice`
`IStream.getSupportedProfiles`	`IModule.connectExternalDevice`
<`routes`>	`IModule.getAudioRoutes`
`IDevice.createAudioPatch` `IDevice.updateAudioPatch` `IDevice.releaseAudioPatch` `IStream.getDevices` `IStream.setDevices` Specification of the device in `IDevice.openInputStream` `IDevice.openOutputStream`	`IModule.setAudioPatch` `IModule.setAudioPortConfig` `IModule.resetAudioPatch`

Audio port configurations and streams

HIDL API interface methods	AIDL API interface methods
`IStream.getAudioProperties` `IStream.setAudioProperties` `IStreamIn.getAudioSource`	`IModule.getAudioPortConfigs` `IModule.setAudioPortConfig`
`IDevice.openInputStream` `IDevice.openOutputStream` `IStreamIn.prepareForReading` `IStreamOut.prepareForWriting` `IStream.createMmapBuffer`	`IModule.openInputStream` `IModule.openOutputStream`
`IStream.close`	`IStreamCommon.close`
`IStreamIn.updateSinkMetadata` `IStreamOut.updateSourceMetadata`	`IStreamIn.updateMetadata` `IStreamOut.updateMetadata`
`IStream.standby`	`StreamDescriptor.Command.standby`
`IStream.pause` `IStream.resume` `IStream.start` `IStream.stop`	`StreamDescriptor.Command.pause` `.start` `.start` `.drain`
`IStreamOut.drain` `IStreamOut.flush`	`StreamDescriptor.Command.drain` `.flush`
`IStreamOut.setCallback` `IStreamOut.clearCallback`	`IModule.openOutputStream` `IStreamCommon.close`
`IStreamOut.getPresentationPosition` and `IStreamIn.getCapturePosition` `IStreamOut.getLatency` `IStream.getMmapPosition` `IStreamIn.getInputFramesLost`	`StreamDescriptor.Reply.observable` `StreamDescriptor.Reply.latencyMs` `StreamDescriptor.Reply.hardware` `StreamDescriptor.Reply.xrunFrames`
`IDevice.getInputBufferSize` `IStreamOut.getLatency` `IStream.getBufferSize` `IStream.getFrameSize` `IStream.getFrameCount`	`IModule.setAudioPatch`, nominal latency, and minimal buffer size are part of the `AudioPatch` structure returned by the HAL. Actual buffer size in frames is part of the `StreamDescriptor` structure, together with frame size in bytes. Buffer size in bytes can be calculated by multiplying these two numbers.

Audio Effects connection

HIDL API interface methods	AIDL API interface methods
`IDevice.addDeviceEffect` `IDevice.removeDeviceEffect`	`IModule.addDeviceEffect` `IModule.removeDeviceEffect`
`IStream.addEffect` `IStream.removeEffect`	`IStreamCommon.addEffect` `IStreamCommon.removeEffect`

System-wide configuration

System-wide configuration that was previously defined in audio policy XML configuration files (namely, audio_policy_configuration.xml and audio_policy_engine_configuration.xml) must be provided through IConfig. However, to ease the transition to AIDL, vendors still have the option of using the same XML files they previously used to set system-wide configuration. The reference implementation for IConfig contains the code necessary for representing information from the XML file using AIDL data types, which facilitates conversion from XML to AIDL.

HIDL configuration file elements	AIDL API interface methods
`<globalConfiguration>` ~~`<speaker_drc_enabled>`~~¹ `<call_screen_mode_supported>` `<engine_library>`	Separated into two different methods: `ITelephony.getSupportedAudioModes` `IConfig.getEngineConfig`
`<volumes>`, OR `<volumeGroups>`, `<ProductStrategies>`	`IConfig.getEngineConfig`
`<surroundSound>`	`IConfig.getSurroundSoundConfig`

speaker_drc_enabled is removed from the configuration file as this configuration item isn't used within the system. All devices must have DRC enabled.

Feature-related functionality

HIDL API interface methods	AIDL API interface
`IDevice.setMasterVolume` `IDevice.getMasterVolume` `IDevice.setMicMute` `IDevice.getMicMute` `IDevice.setMasterMute` `IDevice.getMasterMute`	`IModule.\*`
`IPrimaryDevice.getTtyMode` `IPrimaryDevice.setTtyMode` `IPrimaryDevice.getHacEnabled` `IPrimaryDevice.setHacEnabled` `IPrimaryDevice.setVoiceVolume`	`ITelephony.TelecomConfig.\*`
`IPrimaryDevice.setBtScoHeadsetDebugName` `IPrimaryDevice.getBtScoNrecEnabled` `IPrimaryDevice.setBtScoNrecEnabled` `IPrimaryDevice.getBtScoWidebandEnabled` `IPrimaryDevice.setBtScoWidebandEnabled,` `IPrimaryDevice.getBtHfpEnabled` `IPrimaryDevice.setBtHfpEnabled` `IPrimaryDevice.setBtHfpSampleRate` `IPrimaryDevice.setBtHfpVolume`	`IBluetooth.ScoConfig.\` `IBluetooth.HfpConfig.\`
`IPrimaryDevice.setMode` `IPrimaryDevice.updateRotation`	`ITelephony.switchAudioMode` `IModule.updateAudioMode` `IModule.updateScreenRotation`
`IDevice.setScreenState` `IDevice.getMicrophones`	`IModule.updateScreenState` `IModule.getMicrophones`
`IDevice.getHwAvSync` `IStream.setHwAvSync`	`IModule.generateHwAvSyncId` `IStreamCommon.updateHwAvSyncId`
`IStreamIn.setGain` `IStreamIn.setMicrophoneDirection` `IStreamIn.setMicrophoneFieldDimension`	`IStreamIn.setHwGain` `IStreamIn.setMicrophoneDirection` `IStreamIn.setMicrophoneFieldDimension`
`IStreamOut.getDualMonoMode` `IStreamOut.setDualMonoMode` `IStreamOut.getPlaybackRateParameters` `IStreamOut.setPlaybackRateParameters` `IStreamOut.selectPresentation` `IStreamOut.getAudioDescriptionMixLevel` `IStreamOut.setAudioDescriptionMixLevel` `IStreamOut.setLatencyMode` `IStreamOut.getRecommendedLatencyModes`	`IStreamOut.\*`
`IStreamOut.setEventCallback` `IStreamOut.setLatencyModeCallback`	`IModule.openOutputStream` (callbacks are combined into `IStreamOutEventCallback`)
`IDevice.get/setParameters` `IStream.get/setParameters`	`IModule.get/setVendorParameters` `IStreamCommon.get/setVendorParameters`

Obsolete methods

HIDL API interface methods	Comments
`IDevice.initCheck` `IDevice.close`	The HAL module publishes itself with the `ServiceManager` only on successful initialization. At that point, it is considered to be permanent and can't be closed.
`IDevice.supportsAudioPatches` `IStreamOut.supportsPauseAndResume` `IStreamOut.supportsDrain`	Support for patches, pause, resume and drain is mandatory.
`IStreamOut.getRenderPosition` `IStreamOut.getNextWriteTimestamp`	Obsolete.

Vendor extensions

In the HIDL API, vendor extensions are implemented using the getParameters or setParameters methods from the IDevice and IStream interfaces. These methods accept arbitrary strings. In the AIDL API, there are corresponding methods, such as getVendorParameters or setVendorParameters, which take arbitrary Parcelable instances by using encapsulation within ParcelableHolders.

Other changes

Other general changes are as follows:

To improve the testability of HAL APIs, in the AIDL version, we introduce debugging options that are used by VTS tests and are available through the ModuleDebug parcelable. These options instruct the HAL to emulate certain functionality (for example, connection of external devices), which otherwise requires manual intervention and use of external testing equipment.
HAL services are required to restart when the value of the system property sys.audio.restart.hal is set to 1. The restart is achieved through audioserver.rc. While implementing the HAL, use the appropriate HAL service name listed in the audioserver.rc file. In Android 14, the name vendor.audio-hal-aidl is added specifically for the AIDL version of the HAL.

Effects HAL

All HIDL interfaces are within the android.hardware.audio.effect@N.M* package, where N.M is the Major.Minor version. All AIDL interfaces are within the android.hardware.audio.effect package.

HIDL API interfaces and configuration files	AIDL API interfaces
`IEffectsFactory`	`IFactory`
`IEffect`	`IEffect`
`audio_effects.xml`	`IEffect`

Effect Factory

HIDL API interfaces (android.hardware.audio.effect@X.X)	AIDL API interfaces (android.hardware.audio.effect)
`IEffectsFactory.getAllDescriptors`	`IFactory.queryEffects` with null UUID parameter
`IEffectsFactory.getDescriptor`	`IFactory.queryEffects` with UUID parameter
`IEffectsFactory.createEffect`	`IFactory.createEffect`
`audio_effects.xml`	`IFactory.queryProcessing` `IFactory.queryEffects`

Effect interfaces

HIDL API interfaces (android.hardware.audio.effect@X.X)	AIDL API interfaces (android.hardware.audio.effect)
`IEffect.init`	`IEffect.open`
`IEffect.setConfig`	`IEffect.setParameter`
`IEffect.enable`	`IEffect.command(CommandId::START)`
`IEffect.disable`	`IEffect.command(CommandId::STOP)`
`IEffect.reset`	`IEffect.command(CommandId::RESET)`
`IEffect.getDescriptor`	`IEffect.getDescriptor`
`IEffect.command`	Map to `IEffect.command`, `IEffect.setParameter`, or `IEffect.getParameter` based on the type of legacy HIDL command
N/A	`IEffect.getState`
`IEffect.setParameter`	`IEffect.setParameter`
`IEffect.getParameter`	`IEffect.getParameter`

Effect Commands

HIDL API interfaces (android.hardware.audio.effect@X.X)	AIDL API interfaces (android.hardware.audio.effect)
`EFFECT_CMD_INIT`	`IEffect.open`
`EFFECT_CMD_RESET`	`CommandId.RESET`
`EFFECT_CMD_ENABLE`	`IEffect.command(CommandId::START)`
`EFFECT_CMD_DISABLE`	`IEffect.command(CommandId::STOP)`
`EFFECT_CMD_SET_PARAM_DEFERRED`	Deprecated in Effects AIDL HAL
`EFFECT_CMD_SET_PARAM_COMMIT`	Deprecated in Effects AIDL HAL
`EFFECT_CMD_SET_CONFIG` `EFFECT_CMD_SET_PARAM` `EFFECT_CMD_SET_DEVICE` `EFFECT_CMD_SET_VOLUME` `EFFECT_CMD_SET_AUDIO_MODE` `EFFECT_CMD_SET_CONFIG_REVERSE` `EFFECT_CMD_SET_INPUT_DEVICE` `EFFECT_CMD_SET_FEATURE_CONFIG` `EFFECT_CMD_SET_AUDIO_SOURCE`	`IEffect.setParameter`
`EFFECT_CMD_GET_PARAM` `EFFECT_CMD_GET_CONFIG` `EFFECT_CMD_GET_CONFIG_REVERSE` `EFFECT_CMD_GET_FEATURE_SUPPORTED_CONFIGS` `EFFECT_CMD_GET_FEATURE_CONFIG` `VISUALIZER_CMD_MEASURE` `EFFECT_CMD_FIRST_PROPRIETARY` (same as `VISUALIZER_CMD_CAPTURE`)	`IEffect.getParameter`
`EFFECT_CMD_OFFLOAD`	Deprecated. In AIDL, offload and non-offload mode switches are handled in the framework.
`EFFECT_CMD_DUMP`	Handled by the built-in binder transaction `AIBinder_dump`.

Common Effect parameters definition

HIDL definition (android.hardware.audio.effect@X.X)	AIDL definition
`Types.hal`	`Flags.aidl` `Parameter.aidl`

Specific Effects definition

HIDL API interfaces (android.hardware.audio.effect@X.X)	AIDL API interfaces (android.hardware.audio.effect)
`I$EffectType$.hal`	`$EffectType$.aidl`