diff --git a/audio/7.0/IStream.hal b/audio/7.0/IStream.hal
index ab9aa7d..393e38f 100644
--- a/audio/7.0/IStream.hal
+++ b/audio/7.0/IStream.hal
@@ -73,14 +73,14 @@
 
     /**
      * Sets stream parameters. Only sets parameters that are specified.
-     * See the description of AudioConfigBase for the details.
      *
      * Optional method. If implemented, only called on a stopped stream.
      *
      * @param config basic stream configuration.
      * @return retval operation completion status.
      */
-    setAudioProperties(AudioConfigBase config) generates (Result retval);
+    setAudioProperties(AudioConfigBaseOptional config)
+            generates (Result retval);
 
     /**
      * Applies audio effect to the stream.
diff --git a/audio/7.0/config/api/current.txt b/audio/7.0/config/api/current.txt
index 1da8b09..8a4662f 100644
--- a/audio/7.0/config/api/current.txt
+++ b/audio/7.0/config/api/current.txt
@@ -198,6 +198,7 @@
     enum_constant public static final android.audio.policy.configuration.V7_0.AudioFormat AUDIO_FORMAT_APTX_HD;
     enum_constant public static final android.audio.policy.configuration.V7_0.AudioFormat AUDIO_FORMAT_APTX_TWSP;
     enum_constant public static final android.audio.policy.configuration.V7_0.AudioFormat AUDIO_FORMAT_CELT;
+    enum_constant public static final android.audio.policy.configuration.V7_0.AudioFormat AUDIO_FORMAT_DEFAULT;
     enum_constant public static final android.audio.policy.configuration.V7_0.AudioFormat AUDIO_FORMAT_DOLBY_TRUEHD;
     enum_constant public static final android.audio.policy.configuration.V7_0.AudioFormat AUDIO_FORMAT_DSD;
     enum_constant public static final android.audio.policy.configuration.V7_0.AudioFormat AUDIO_FORMAT_DTS;
diff --git a/audio/7.0/config/audio_policy_configuration.xsd b/audio/7.0/config/audio_policy_configuration.xsd
index 56b3a27..685e84a 100644
--- a/audio/7.0/config/audio_policy_configuration.xsd
+++ b/audio/7.0/config/audio_policy_configuration.xsd
@@ -329,6 +329,7 @@
     </xs:simpleType>
     <xs:simpleType name="audioFormat">
         <xs:restriction base="xs:string">
+            <xs:enumeration value="AUDIO_FORMAT_DEFAULT" />
             <xs:enumeration value="AUDIO_FORMAT_PCM_16_BIT" />
             <xs:enumeration value="AUDIO_FORMAT_PCM_8_BIT"/>
             <xs:enumeration value="AUDIO_FORMAT_PCM_32_BIT"/>
diff --git a/audio/common/7.0/example/Effect.cpp b/audio/common/7.0/example/Effect.cpp
index 27f28c6..5788811 100644
--- a/audio/common/7.0/example/Effect.cpp
+++ b/audio/common/7.0/example/Effect.cpp
@@ -107,14 +107,13 @@
 }
 
 Return<void> Effect::getConfig(getConfig_cb _hidl_cb) {
-    const EffectConfig config = {
-            {} /* inputCfg */,
-            // outputCfg
-            {{} /* buffer */,
-             {toString(xsd::AudioFormat::AUDIO_FORMAT_PCM_16_BIT), 48000 /* samplingRateHz */,
-              toString(xsd::AudioChannelMask::AUDIO_CHANNEL_OUT_STEREO)}, /* base */
-             EffectBufferAccess::ACCESS_ACCUMULATE,
-             0 /* mask */}};
+    EffectConfig config;
+    // inputCfg left unspecified.
+    config.outputCfg.base.format.value(toString(xsd::AudioFormat::AUDIO_FORMAT_PCM_16_BIT));
+    config.outputCfg.base.sampleRateHz.value(48000);
+    config.outputCfg.base.channelMask.value(
+            toString(xsd::AudioChannelMask::AUDIO_CHANNEL_OUT_STEREO));
+    config.outputCfg.accessMode.value(EffectBufferAccess::ACCESS_ACCUMULATE);
     _hidl_cb(Result::OK, config);
     return Void();
 }
diff --git a/audio/common/7.0/types.hal b/audio/common/7.0/types.hal
index ed6d94f..3903a0b 100644
--- a/audio/common/7.0/types.hal
+++ b/audio/common/7.0/types.hal
@@ -118,9 +118,28 @@
  * Base configuration attributes applicable to any stream of audio.
  */
 struct AudioConfigBase {
-    AudioFormat format;                 // empty means 'unspecified'
-    uint32_t sampleRateHz;              // 0 means 'unspecified'
-    AudioChannelMask channelMask;       // empty means 'unspecified'
+    AudioFormat format;
+    uint32_t sampleRateHz;
+    AudioChannelMask channelMask;
+};
+
+/**
+ * Base configuration attributes applicable to any stream of audio.
+ * Any attribute may be left unspecified.
+ */
+struct AudioConfigBaseOptional {
+    safe_union Format {
+        Monostate unspecified;
+        AudioFormat value;
+    } format;
+    safe_union SampleRate {
+        Monostate unspecified;
+        uint32_t value;
+    } sampleRateHz;
+    safe_union ChannelMask {
+        Monostate unspecified;
+        AudioChannelMask value;
+    } channelMask;
 };
 
 /**
@@ -439,11 +458,9 @@
      */
     AudioPortHandle id;
     /**
-     * Basic parameters: sampling rate, format, channel mask. Only some of the
-     * parameters (or none) may be set. See the documentation of the
-     * AudioConfigBase struct.
+     * Basic parameters: sampling rate, format, channel mask.
      */
-    AudioConfigBase base;
+    AudioConfigBaseOptional base;
     /** Associated gain control. */
     safe_union OptionalGain {
         Monostate unspecified;
diff --git a/audio/common/all-versions/default/7.0/HidlUtils.cpp b/audio/common/all-versions/default/7.0/HidlUtils.cpp
index de19faf..f09db5e 100644
--- a/audio/common/all-versions/default/7.0/HidlUtils.cpp
+++ b/audio/common/all-versions/default/7.0/HidlUtils.cpp
@@ -147,6 +147,59 @@
     return result;
 }
 
+status_t HidlUtils::audioConfigBaseOptionalFromHal(const audio_config_base_t& halConfigBase,
+                                                   bool isInput, bool formatSpecified,
+                                                   bool sampleRateSpecified,
+                                                   bool channelMaskSpecified,
+                                                   AudioConfigBaseOptional* configBase) {
+    status_t result = NO_ERROR;
+    if (formatSpecified) {
+        AudioFormat value;
+        CONVERT_CHECKED(audioFormatFromHal(halConfigBase.format, &value), result);
+        configBase->format.value(std::move(value));
+    } else {
+        configBase->format.unspecified({});
+    }
+    if (sampleRateSpecified) {
+        configBase->sampleRateHz.value(halConfigBase.sample_rate);
+    } else {
+        configBase->sampleRateHz.unspecified({});
+    }
+    if (channelMaskSpecified) {
+        AudioChannelMask value;
+        CONVERT_CHECKED(audioChannelMaskFromHal(halConfigBase.channel_mask, isInput, &value),
+                        result);
+        configBase->channelMask.value(std::move(value));
+    }
+    return result;
+}
+
+status_t HidlUtils::audioConfigBaseOptionalToHal(const AudioConfigBaseOptional& configBase,
+                                                 audio_config_base_t* halConfigBase,
+                                                 bool* formatSpecified, bool* sampleRateSpecified,
+                                                 bool* channelMaskSpecified) {
+    status_t result = NO_ERROR;
+    *formatSpecified = configBase.format.getDiscriminator() ==
+                       AudioConfigBaseOptional::Format::hidl_discriminator::value;
+    if (*formatSpecified) {
+        CONVERT_CHECKED(audioFormatToHal(configBase.format.value(), &halConfigBase->format),
+                        result);
+    }
+    *sampleRateSpecified = configBase.sampleRateHz.getDiscriminator() ==
+                           AudioConfigBaseOptional::SampleRate::hidl_discriminator::value;
+    if (*sampleRateSpecified) {
+        halConfigBase->sample_rate = configBase.sampleRateHz.value();
+    }
+    *channelMaskSpecified = configBase.channelMask.getDiscriminator() ==
+                            AudioConfigBaseOptional::ChannelMask::hidl_discriminator::value;
+    if (*channelMaskSpecified) {
+        CONVERT_CHECKED(
+                audioChannelMaskToHal(configBase.channelMask.value(), &halConfigBase->channel_mask),
+                result);
+    }
+    return result;
+}
+
 status_t HidlUtils::audioContentTypeFromHal(const audio_content_type_t halContentType,
                                             AudioContentType* contentType) {
     *contentType = audio_content_type_to_string(halContentType);
@@ -508,23 +561,14 @@
               audio_port_config_has_input_direction(&halConfig), isInput);
         result = BAD_VALUE;
     }
-    if (halConfig.config_mask & AUDIO_PORT_CONFIG_SAMPLE_RATE) {
-        config->base.sampleRateHz = halConfig.sample_rate;
-    } else {
-        config->base.sampleRateHz = {};
-    }
-    if (halConfig.config_mask & AUDIO_PORT_CONFIG_CHANNEL_MASK) {
-        CONVERT_CHECKED(
-                audioChannelMaskFromHal(halConfig.channel_mask, isInput, &config->base.channelMask),
-                result);
-    } else {
-        config->base.channelMask = {};
-    }
-    if (halConfig.config_mask & AUDIO_PORT_CONFIG_FORMAT) {
-        CONVERT_CHECKED(audioFormatFromHal(halConfig.format, &config->base.format), result);
-    } else {
-        config->base.format = {};
-    }
+    audio_config_base_t halConfigBase = {halConfig.sample_rate, halConfig.channel_mask,
+                                         halConfig.format};
+    CONVERT_CHECKED(
+            audioConfigBaseOptionalFromHal(
+                    halConfigBase, isInput, halConfig.config_mask & AUDIO_PORT_CONFIG_FORMAT,
+                    halConfig.config_mask & AUDIO_PORT_CONFIG_SAMPLE_RATE,
+                    halConfig.config_mask & AUDIO_PORT_CONFIG_CHANNEL_MASK, &config->base),
+            result);
     if (halConfig.config_mask & AUDIO_PORT_CONFIG_GAIN) {
         config->gain.config({});
         CONVERT_CHECKED(audioGainConfigFromHal(halConfig.gain, isInput, &config->gain.config()),
@@ -540,19 +584,23 @@
     status_t result = NO_ERROR;
     memset(halConfig, 0, sizeof(audio_port_config));
     halConfig->id = config.id;
-    halConfig->config_mask = {};
-    if (config.base.sampleRateHz != 0) {
+    halConfig->config_mask = 0;
+    audio_config_base_t halConfigBase = AUDIO_CONFIG_BASE_INITIALIZER;
+    bool formatSpecified = false, sRateSpecified = false, channelMaskSpecified = false;
+    CONVERT_CHECKED(audioConfigBaseOptionalToHal(config.base, &halConfigBase, &formatSpecified,
+                                                 &sRateSpecified, &channelMaskSpecified),
+                    result);
+    if (sRateSpecified) {
         halConfig->config_mask |= AUDIO_PORT_CONFIG_SAMPLE_RATE;
-        halConfig->sample_rate = config.base.sampleRateHz;
+        halConfig->sample_rate = halConfigBase.sample_rate;
     }
-    if (!config.base.channelMask.empty()) {
+    if (channelMaskSpecified) {
         halConfig->config_mask |= AUDIO_PORT_CONFIG_CHANNEL_MASK;
-        CONVERT_CHECKED(audioChannelMaskToHal(config.base.channelMask, &halConfig->channel_mask),
-                        result);
+        halConfig->channel_mask = halConfigBase.channel_mask;
     }
-    if (!config.base.format.empty()) {
+    if (formatSpecified) {
         halConfig->config_mask |= AUDIO_PORT_CONFIG_FORMAT;
-        CONVERT_CHECKED(audioFormatToHal(config.base.format, &halConfig->format), result);
+        halConfig->format = halConfigBase.format;
     }
     if (config.gain.getDiscriminator() ==
         AudioPortConfig::OptionalGain::hidl_discriminator::config) {
diff --git a/audio/common/all-versions/default/HidlUtils.h b/audio/common/all-versions/default/HidlUtils.h
index 8e9275c..cc4fbf2 100644
--- a/audio/common/all-versions/default/HidlUtils.h
+++ b/audio/common/all-versions/default/HidlUtils.h
@@ -89,6 +89,15 @@
                                            AudioConfigBase* configBase);
     static status_t audioConfigBaseToHal(const AudioConfigBase& configBase,
                                          audio_config_base_t* halConfigBase);
+    static status_t audioConfigBaseOptionalFromHal(const audio_config_base_t& halConfigBase,
+                                                   bool isInput, bool formatSpecified,
+                                                   bool sampleRateSpecified,
+                                                   bool channelMaskSpecified,
+                                                   AudioConfigBaseOptional* configBase);
+    static status_t audioConfigBaseOptionalToHal(const AudioConfigBaseOptional& configBase,
+                                                 audio_config_base_t* halConfigBase,
+                                                 bool* formatSpecified, bool* sampleRateSpecified,
+                                                 bool* channelMaskSpecified);
     static status_t audioDeviceTypeFromHal(audio_devices_t halDevice, AudioDevice* device);
     static status_t audioDeviceTypeToHal(const AudioDevice& device, audio_devices_t* halDevice);
     static status_t audioFormatFromHal(audio_format_t halFormat, AudioFormat* format);
diff --git a/audio/common/all-versions/default/tests/hidlutils_tests.cpp b/audio/common/all-versions/default/tests/hidlutils_tests.cpp
index fef88b4..642ece3 100644
--- a/audio/common/all-versions/default/tests/hidlutils_tests.cpp
+++ b/audio/common/all-versions/default/tests/hidlutils_tests.cpp
@@ -35,30 +35,27 @@
 using namespace ::android::audio::policy::configuration::V7_0;
 }
 
-static constexpr audio_channel_mask_t kInvalidHalChannelMask =
-        static_cast<audio_channel_mask_t>(0xFFFFFFFFU);
+static constexpr audio_channel_mask_t kInvalidHalChannelMask = AUDIO_CHANNEL_INVALID;
 static constexpr audio_content_type_t kInvalidHalContentType =
         static_cast<audio_content_type_t>(0xFFFFFFFFU);
 static constexpr audio_devices_t kInvalidHalDevice = static_cast<audio_devices_t>(0xFFFFFFFFU);
-static constexpr audio_format_t kInvalidHalFormat = static_cast<audio_format_t>(0xFFFFFFFFU);
+static constexpr audio_format_t kInvalidHalFormat = AUDIO_FORMAT_INVALID;
 static constexpr audio_gain_mode_t kInvalidHalGainMode =
         static_cast<audio_gain_mode_t>(0xFFFFFFFFU);
-static constexpr audio_source_t kInvalidHalSource = static_cast<audio_source_t>(0xFFFFFFFFU);
+// AUDIO_SOURCE_INVALID is framework-only.
+static constexpr audio_source_t kInvalidHalSource = static_cast<audio_source_t>(-1);
 static constexpr audio_stream_type_t kInvalidHalStreamType =
         static_cast<audio_stream_type_t>(0xFFFFFFFFU);
 static constexpr audio_usage_t kInvalidHalUsage = static_cast<audio_usage_t>(0xFFFFFFFFU);
 
 TEST(HidlUtils, ConvertInvalidChannelMask) {
     AudioChannelMask invalid;
-    EXPECT_EQ(BAD_VALUE, HidlUtils::audioChannelMaskFromHal(AUDIO_CHANNEL_INVALID,
-                                                            false /*isInput*/, &invalid));
-    EXPECT_EQ(BAD_VALUE, HidlUtils::audioChannelMaskFromHal(AUDIO_CHANNEL_INVALID, true /*isInput*/,
-                                                            &invalid));
     EXPECT_EQ(BAD_VALUE, HidlUtils::audioChannelMaskFromHal(kInvalidHalChannelMask,
                                                             false /*isInput*/, &invalid));
     EXPECT_EQ(BAD_VALUE, HidlUtils::audioChannelMaskFromHal(kInvalidHalChannelMask,
                                                             true /*isInput*/, &invalid));
     audio_channel_mask_t halInvalid;
+    EXPECT_EQ(BAD_VALUE, HidlUtils::audioChannelMaskToHal("", &halInvalid));
     // INVALID channel mask is not in XSD thus it's not allowed for transfer over HIDL.
     EXPECT_EQ(BAD_VALUE, HidlUtils::audioChannelMaskToHal("AUDIO_CHANNEL_INVALID", &halInvalid));
     EXPECT_EQ(BAD_VALUE, HidlUtils::audioChannelMaskToHal("random string", &halInvalid));
@@ -148,40 +145,241 @@
     }
 }
 
+static AudioConfigBase generateValidConfigBase(bool isInput) {
+    AudioConfigBase configBase;
+    configBase.sampleRateHz = 44100;
+    configBase.format = toString(xsd::AudioFormat::AUDIO_FORMAT_PCM_16_BIT);
+    configBase.channelMask = isInput ? toString(xsd::AudioChannelMask::AUDIO_CHANNEL_IN_STEREO)
+                                     : toString(xsd::AudioChannelMask::AUDIO_CHANNEL_OUT_STEREO);
+    return configBase;
+}
+
 TEST(HidlUtils, ConvertInvalidConfigBase) {
     AudioConfigBase invalid;
-    EXPECT_EQ(BAD_VALUE, HidlUtils::audioConfigBaseFromHal({.sample_rate = 0,
-                                                            .channel_mask = kInvalidHalChannelMask,
-                                                            .format = kInvalidHalFormat},
-                                                           false /*isInput*/, &invalid));
-    EXPECT_EQ(BAD_VALUE, HidlUtils::audioConfigBaseFromHal({.sample_rate = 0,
-                                                            .channel_mask = kInvalidHalChannelMask,
-                                                            .format = kInvalidHalFormat},
-                                                           true /*isInput*/, &invalid));
+    audio_config_base_t halInvalidChannelMask = AUDIO_CONFIG_BASE_INITIALIZER;
+    halInvalidChannelMask.channel_mask = kInvalidHalChannelMask;
+    EXPECT_EQ(BAD_VALUE, HidlUtils::audioConfigBaseFromHal(halInvalidChannelMask, false /*isInput*/,
+                                                           &invalid));
+    EXPECT_EQ(BAD_VALUE,
+              HidlUtils::audioConfigBaseFromHal(halInvalidChannelMask, true /*isInput*/, &invalid));
+    audio_config_base_t halInvalidFormat = AUDIO_CONFIG_BASE_INITIALIZER;
+    halInvalidFormat.format = kInvalidHalFormat;
+    EXPECT_EQ(BAD_VALUE,
+              HidlUtils::audioConfigBaseFromHal(halInvalidFormat, false /*isInput*/, &invalid));
+    EXPECT_EQ(BAD_VALUE,
+              HidlUtils::audioConfigBaseFromHal(halInvalidFormat, true /*isInput*/, &invalid));
+
     audio_config_base_t halInvalid;
-    invalid.sampleRateHz = 0;
-    invalid.channelMask = "random string";
-    invalid.format = "random string";
-    EXPECT_EQ(BAD_VALUE, HidlUtils::audioConfigBaseToHal(invalid, &halInvalid));
+    AudioConfigBase invalidChannelMask = generateValidConfigBase(false /*isInput*/);
+    invalidChannelMask.channelMask = "random string";
+    EXPECT_EQ(BAD_VALUE, HidlUtils::audioConfigBaseToHal(invalidChannelMask, &halInvalid));
+    AudioConfigBase invalidFormat = generateValidConfigBase(false /*isInput*/);
+    invalidFormat.format = "random string";
+    EXPECT_EQ(BAD_VALUE, HidlUtils::audioConfigBaseToHal(invalidFormat, &halInvalid));
+}
+
+TEST(HidlUtils, ConvertConfigBaseDefault) {
+    audio_config_base_t halBaseDefault = AUDIO_CONFIG_BASE_INITIALIZER;
+    AudioConfigBase baseDefaultOut, baseDefaultIn;
+    EXPECT_EQ(NO_ERROR, HidlUtils::audioConfigBaseFromHal(halBaseDefault, false /*isInput*/,
+                                                          &baseDefaultOut));
+    EXPECT_EQ(NO_ERROR,
+              HidlUtils::audioConfigBaseFromHal(halBaseDefault, true /*isInput*/, &baseDefaultIn));
+    EXPECT_EQ(baseDefaultOut, baseDefaultIn);
+    audio_config_base_t halBaseDefaultBack;
+    EXPECT_EQ(NO_ERROR, HidlUtils::audioConfigBaseToHal(baseDefaultOut, &halBaseDefaultBack));
+    EXPECT_EQ(halBaseDefault.sample_rate, halBaseDefaultBack.sample_rate);
+    EXPECT_EQ(halBaseDefault.channel_mask, halBaseDefaultBack.channel_mask);
+    EXPECT_EQ(halBaseDefault.format, halBaseDefaultBack.format);
 }
 
 TEST(HidlUtils, ConvertConfigBase) {
-    AudioConfigBase configBase;
-    configBase.sampleRateHz = 44100;
-    configBase.channelMask = toString(xsd::AudioChannelMask::AUDIO_CHANNEL_OUT_STEREO);
-    configBase.format = toString(xsd::AudioFormat::AUDIO_FORMAT_PCM_16_BIT);
-    audio_config_base_t halConfigBase;
-    EXPECT_EQ(NO_ERROR, HidlUtils::audioConfigBaseToHal(configBase, &halConfigBase));
-    AudioConfigBase configBaseBack;
+    AudioConfigBase configBaseOut = generateValidConfigBase(false /*isInput*/);
+    audio_config_base_t halConfigBaseOut;
+    EXPECT_EQ(NO_ERROR, HidlUtils::audioConfigBaseToHal(configBaseOut, &halConfigBaseOut));
+    AudioConfigBase configBaseOutBack;
+    EXPECT_EQ(NO_ERROR, HidlUtils::audioConfigBaseFromHal(halConfigBaseOut, false /*isInput*/,
+                                                          &configBaseOutBack));
+    EXPECT_EQ(configBaseOut, configBaseOutBack);
+
+    AudioConfigBase configBaseIn = generateValidConfigBase(true /*isInput*/);
+    audio_config_base_t halConfigBaseIn;
+    EXPECT_EQ(NO_ERROR, HidlUtils::audioConfigBaseToHal(configBaseIn, &halConfigBaseIn));
+    AudioConfigBase configBaseInBack;
+    EXPECT_EQ(NO_ERROR, HidlUtils::audioConfigBaseFromHal(halConfigBaseIn, true /*isInput*/,
+                                                          &configBaseInBack));
+    EXPECT_EQ(configBaseIn, configBaseInBack);
+}
+
+TEST(HidlUtils, ConvertInvalidConfigBaseOptional) {
+    AudioConfigBaseOptional invalid;
+    audio_config_base_t halInvalidChannelMask = AUDIO_CONFIG_BASE_INITIALIZER;
+    halInvalidChannelMask.channel_mask = kInvalidHalChannelMask;
+    EXPECT_EQ(BAD_VALUE,
+              HidlUtils::audioConfigBaseOptionalFromHal(
+                      halInvalidChannelMask, false /*isInput*/, false /*formatSpecified*/,
+                      false /*sampleRateSpecified*/, true /*channelMaskSpecified*/, &invalid));
+    EXPECT_EQ(BAD_VALUE,
+              HidlUtils::audioConfigBaseOptionalFromHal(
+                      halInvalidChannelMask, true /*isInput*/, false /*formatSpecified*/,
+                      false /*sampleRateSpecified*/, true /*channelMaskSpecified*/, &invalid));
+    // Unspecified invalid values are ignored
+    AudioConfigBaseOptional unspecified;
     EXPECT_EQ(NO_ERROR,
-              HidlUtils::audioConfigBaseFromHal(halConfigBase, false /*isInput*/, &configBaseBack));
-    EXPECT_EQ(configBase, configBaseBack);
+              HidlUtils::audioConfigBaseOptionalFromHal(
+                      halInvalidChannelMask, false /*isInput*/, false /*formatSpecified*/,
+                      false /*sampleRateSpecified*/, false /*channelMaskSpecified*/, &unspecified));
+    EXPECT_EQ(NO_ERROR,
+              HidlUtils::audioConfigBaseOptionalFromHal(
+                      halInvalidChannelMask, true /*isInput*/, false /*formatSpecified*/,
+                      false /*sampleRateSpecified*/, false /*channelMaskSpecified*/, &unspecified));
+    audio_config_base_t halInvalidFormat = AUDIO_CONFIG_BASE_INITIALIZER;
+    halInvalidFormat.format = kInvalidHalFormat;
+    EXPECT_EQ(BAD_VALUE,
+              HidlUtils::audioConfigBaseOptionalFromHal(
+                      halInvalidFormat, false /*isInput*/, true /*formatSpecified*/,
+                      false /*sampleRateSpecified*/, false /*channelMaskSpecified*/, &invalid));
+    EXPECT_EQ(BAD_VALUE,
+              HidlUtils::audioConfigBaseOptionalFromHal(
+                      halInvalidFormat, true /*isInput*/, true /*formatSpecified*/,
+                      false /*sampleRateSpecified*/, false /*channelMaskSpecified*/, &invalid));
+    EXPECT_EQ(NO_ERROR,
+              HidlUtils::audioConfigBaseOptionalFromHal(
+                      halInvalidFormat, false /*isInput*/, false /*formatSpecified*/,
+                      false /*sampleRateSpecified*/, false /*channelMaskSpecified*/, &unspecified));
+    EXPECT_EQ(NO_ERROR,
+              HidlUtils::audioConfigBaseOptionalFromHal(
+                      halInvalidFormat, true /*isInput*/, false /*formatSpecified*/,
+                      false /*sampleRateSpecified*/, false /*channelMaskSpecified*/, &unspecified));
+
+    audio_config_base_t halInvalid;
+    AudioConfigBaseOptional invalidChannelMask;
+    bool formatSpecified, sampleRateSpecified, channelMaskSpecified;
+    invalidChannelMask.channelMask.value("random string");
+    EXPECT_EQ(BAD_VALUE, HidlUtils::audioConfigBaseOptionalToHal(
+                                 invalidChannelMask, &halInvalid, &formatSpecified,
+                                 &sampleRateSpecified, &channelMaskSpecified));
+    AudioConfigBaseOptional invalidFormat;
+    invalidFormat.format.value("random string");
+    EXPECT_EQ(BAD_VALUE,
+              HidlUtils::audioConfigBaseOptionalToHal(invalidFormat, &halInvalid, &formatSpecified,
+                                                      &sampleRateSpecified, &channelMaskSpecified));
+}
+
+TEST(HidlUtils, ConvertConfigBaseOptionalDefault) {
+    audio_config_base_t halBaseDefault = AUDIO_CONFIG_BASE_INITIALIZER;
+    AudioConfigBaseOptional baseDefaultUnspecOut, baseDefaultUnspecIn;
+    EXPECT_EQ(NO_ERROR, HidlUtils::audioConfigBaseOptionalFromHal(
+                                halBaseDefault, false /*isInput*/, false /*formatSpecified*/,
+                                false /*sampleRateSpecified*/, false /*channelMaskSpecified*/,
+                                &baseDefaultUnspecOut));
+    EXPECT_EQ(NO_ERROR, HidlUtils::audioConfigBaseOptionalFromHal(
+                                halBaseDefault, true /*isInput*/, false /*formatSpecified*/,
+                                false /*sampleRateSpecified*/, false /*channelMaskSpecified*/,
+                                &baseDefaultUnspecIn));
+    EXPECT_EQ(baseDefaultUnspecOut, baseDefaultUnspecIn);
+    audio_config_base_t halBaseDefaultUnspecBack = AUDIO_CONFIG_BASE_INITIALIZER;
+    bool formatSpecified, sampleRateSpecified, channelMaskSpecified;
+    EXPECT_EQ(NO_ERROR, HidlUtils::audioConfigBaseOptionalToHal(
+                                baseDefaultUnspecOut, &halBaseDefaultUnspecBack, &formatSpecified,
+                                &sampleRateSpecified, &channelMaskSpecified));
+    EXPECT_FALSE(formatSpecified);
+    EXPECT_FALSE(sampleRateSpecified);
+    EXPECT_FALSE(channelMaskSpecified);
+    EXPECT_EQ(halBaseDefault.sample_rate, halBaseDefaultUnspecBack.sample_rate);
+    EXPECT_EQ(halBaseDefault.channel_mask, halBaseDefaultUnspecBack.channel_mask);
+    EXPECT_EQ(halBaseDefault.format, halBaseDefaultUnspecBack.format);
+
+    AudioConfigBaseOptional baseDefaultSpecOut, baseDefaultSpecIn;
+    EXPECT_EQ(NO_ERROR, HidlUtils::audioConfigBaseOptionalFromHal(
+                                halBaseDefault, false /*isInput*/, true /*formatSpecified*/,
+                                true /*sampleRateSpecified*/, true /*channelMaskSpecified*/,
+                                &baseDefaultSpecOut));
+    EXPECT_EQ(NO_ERROR, HidlUtils::audioConfigBaseOptionalFromHal(
+                                halBaseDefault, true /*isInput*/, true /*formatSpecified*/,
+                                true /*sampleRateSpecified*/, true /*channelMaskSpecified*/,
+                                &baseDefaultSpecIn));
+    EXPECT_EQ(baseDefaultSpecOut, baseDefaultSpecIn);
+    audio_config_base_t halBaseDefaultSpecBack;
+    EXPECT_EQ(NO_ERROR, HidlUtils::audioConfigBaseOptionalToHal(
+                                baseDefaultSpecOut, &halBaseDefaultSpecBack, &formatSpecified,
+                                &sampleRateSpecified, &channelMaskSpecified));
+    EXPECT_TRUE(formatSpecified);
+    EXPECT_TRUE(sampleRateSpecified);
+    EXPECT_TRUE(channelMaskSpecified);
+    EXPECT_EQ(halBaseDefault.sample_rate, halBaseDefaultSpecBack.sample_rate);
+    EXPECT_EQ(halBaseDefault.channel_mask, halBaseDefaultSpecBack.channel_mask);
+    EXPECT_EQ(halBaseDefault.format, halBaseDefaultSpecBack.format);
+}
+
+TEST(HidlUtils, ConvertConfigBaseOptionalEmpty) {
+    AudioConfigBaseOptional empty;
+    bool formatSpecified, sampleRateSpecified, channelMaskSpecified;
+    audio_config_base_t halEmpty = AUDIO_CONFIG_BASE_INITIALIZER;
+    EXPECT_EQ(NO_ERROR,
+              HidlUtils::audioConfigBaseOptionalToHal(empty, &halEmpty, &formatSpecified,
+                                                      &sampleRateSpecified, &channelMaskSpecified));
+    EXPECT_FALSE(formatSpecified);
+    EXPECT_FALSE(sampleRateSpecified);
+    EXPECT_FALSE(channelMaskSpecified);
+    AudioConfigBaseOptional emptyOutBack, emptyInBack;
+    EXPECT_EQ(NO_ERROR, HidlUtils::audioConfigBaseOptionalFromHal(
+                                halEmpty, false /*isInput*/, formatSpecified, sampleRateSpecified,
+                                channelMaskSpecified, &emptyOutBack));
+    EXPECT_EQ(NO_ERROR, HidlUtils::audioConfigBaseOptionalFromHal(
+                                halEmpty, true /*isInput*/, formatSpecified, sampleRateSpecified,
+                                channelMaskSpecified, &emptyInBack));
+    EXPECT_EQ(emptyOutBack, emptyInBack);
+    EXPECT_EQ(empty, emptyOutBack);
+}
+
+TEST(HidlUtils, ConvertConfigBaseOptional) {
+    AudioConfigBase validBaseOut = generateValidConfigBase(false /*isInput*/);
+    AudioConfigBaseOptional configBaseOut;
+    configBaseOut.format.value(validBaseOut.format);
+    configBaseOut.sampleRateHz.value(validBaseOut.sampleRateHz);
+    configBaseOut.channelMask.value(validBaseOut.channelMask);
+    audio_config_base_t halConfigBaseOut;
+    bool formatSpecified, sampleRateSpecified, channelMaskSpecified;
+    EXPECT_EQ(NO_ERROR, HidlUtils::audioConfigBaseOptionalToHal(
+                                configBaseOut, &halConfigBaseOut, &formatSpecified,
+                                &sampleRateSpecified, &channelMaskSpecified));
+    EXPECT_TRUE(formatSpecified);
+    EXPECT_TRUE(sampleRateSpecified);
+    EXPECT_TRUE(channelMaskSpecified);
+    AudioConfigBaseOptional configBaseOutBack;
+    EXPECT_EQ(NO_ERROR, HidlUtils::audioConfigBaseOptionalFromHal(
+                                halConfigBaseOut, false /*isInput*/, formatSpecified,
+                                sampleRateSpecified, channelMaskSpecified, &configBaseOutBack));
+    EXPECT_EQ(configBaseOut, configBaseOutBack);
+
+    AudioConfigBase validBaseIn = generateValidConfigBase(true /*isInput*/);
+    AudioConfigBaseOptional configBaseIn;
+    configBaseIn.format.value(validBaseIn.format);
+    configBaseIn.sampleRateHz.value(validBaseIn.sampleRateHz);
+    configBaseIn.channelMask.value(validBaseIn.channelMask);
+    audio_config_base_t halConfigBaseIn;
+    formatSpecified = false;
+    sampleRateSpecified = false;
+    channelMaskSpecified = false;
+    EXPECT_EQ(NO_ERROR, HidlUtils::audioConfigBaseOptionalToHal(
+                                configBaseIn, &halConfigBaseIn, &formatSpecified,
+                                &sampleRateSpecified, &channelMaskSpecified));
+    EXPECT_TRUE(formatSpecified);
+    EXPECT_TRUE(sampleRateSpecified);
+    EXPECT_TRUE(channelMaskSpecified);
+    AudioConfigBaseOptional configBaseInBack;
+    EXPECT_EQ(NO_ERROR, HidlUtils::audioConfigBaseOptionalFromHal(
+                                halConfigBaseIn, true /*isInput*/, formatSpecified,
+                                sampleRateSpecified, channelMaskSpecified, &configBaseInBack));
+    EXPECT_EQ(configBaseIn, configBaseInBack);
 }
 
 TEST(HidlUtils, ConvertInvalidContentType) {
     AudioContentType invalid;
     EXPECT_EQ(BAD_VALUE, HidlUtils::audioContentTypeFromHal(kInvalidHalContentType, &invalid));
     audio_content_type_t halInvalid;
+    EXPECT_EQ(BAD_VALUE, HidlUtils::audioContentTypeToHal("", &halInvalid));
     EXPECT_EQ(BAD_VALUE, HidlUtils::audioContentTypeToHal("random string", &halInvalid));
 }
 
@@ -202,6 +400,7 @@
     AudioDevice invalid;
     EXPECT_EQ(BAD_VALUE, HidlUtils::audioDeviceTypeFromHal(kInvalidHalDevice, &invalid));
     audio_devices_t halInvalid;
+    EXPECT_EQ(BAD_VALUE, HidlUtils::audioDeviceTypeToHal("", &halInvalid));
     EXPECT_EQ(BAD_VALUE, HidlUtils::audioDeviceTypeToHal("random string", &halInvalid));
 }
 
@@ -233,6 +432,7 @@
 // The enums module is too small to have unit tests on its own.
 TEST(HidlUtils, VendorExtension) {
     EXPECT_TRUE(xsd::isVendorExtension("VX_GOOGLE_VR_42"));
+    EXPECT_FALSE(xsd::isVendorExtension(""));
     EXPECT_FALSE(xsd::isVendorExtension("random string"));
     EXPECT_FALSE(xsd::isVendorExtension("VX_"));
     EXPECT_FALSE(xsd::isVendorExtension("VX_GOOGLE_$$"));
@@ -347,6 +547,9 @@
     AudioFormat invalid;
     EXPECT_EQ(BAD_VALUE, HidlUtils::audioFormatFromHal(kInvalidHalFormat, &invalid));
     audio_format_t halInvalid;
+    EXPECT_EQ(BAD_VALUE, HidlUtils::audioFormatToHal("", &halInvalid));
+    // INVALID format is not in XSD thus it's not allowed for transfer over HIDL.
+    EXPECT_EQ(BAD_VALUE, HidlUtils::audioFormatToHal("AUDIO_FORMAT_INVALID", &halInvalid));
     EXPECT_EQ(BAD_VALUE, HidlUtils::audioFormatToHal("random string", &halInvalid));
 }
 
@@ -357,8 +560,9 @@
         AudioFormat formatBack;
         EXPECT_EQ(NO_ERROR, HidlUtils::audioFormatToHal(format, &halFormat))
                 << "Conversion of \"" << format << "\" failed";
-        EXPECT_TRUE(audio_is_valid_format(halFormat))
-                << "Converted format \"" << format << "\" is invalid";
+        EXPECT_EQ(enumVal != xsd::AudioFormat::AUDIO_FORMAT_DEFAULT,
+                  audio_is_valid_format(halFormat))
+                << "Validity of \"" << format << "\" is not as expected";
         EXPECT_EQ(NO_ERROR, HidlUtils::audioFormatFromHal(halFormat, &formatBack))
                 << "Conversion of format " << halFormat << " failed";
         EXPECT_EQ(format, formatBack);
@@ -430,6 +634,9 @@
     AudioSource invalid;
     EXPECT_EQ(BAD_VALUE, HidlUtils::audioSourceFromHal(kInvalidHalSource, &invalid));
     audio_source_t halInvalid;
+    EXPECT_EQ(BAD_VALUE, HidlUtils::audioSourceToHal("", &halInvalid));
+    // INVALID source is not in XSD thus it's not allowed for transfer over HIDL.
+    EXPECT_EQ(BAD_VALUE, HidlUtils::audioSourceToHal("AUDIO_SOURCE_INVALID", &halInvalid));
     EXPECT_EQ(BAD_VALUE, HidlUtils::audioSourceToHal("random string", &halInvalid));
 }
 
@@ -453,6 +660,7 @@
     AudioStreamType invalid;
     EXPECT_EQ(BAD_VALUE, HidlUtils::audioStreamTypeFromHal(kInvalidHalStreamType, &invalid));
     audio_stream_type_t halInvalid;
+    EXPECT_EQ(BAD_VALUE, HidlUtils::audioStreamTypeToHal("", &halInvalid));
     EXPECT_EQ(BAD_VALUE, HidlUtils::audioStreamTypeToHal("random string", &halInvalid));
 }
 
@@ -524,6 +732,7 @@
     AudioUsage invalid;
     EXPECT_EQ(BAD_VALUE, HidlUtils::audioUsageFromHal(kInvalidHalUsage, &invalid));
     audio_usage_t halInvalid;
+    EXPECT_EQ(BAD_VALUE, HidlUtils::audioUsageToHal("", &halInvalid));
     EXPECT_EQ(BAD_VALUE, HidlUtils::audioUsageToHal("random string", &halInvalid));
 }
 
@@ -543,7 +752,7 @@
 TEST(HidlUtils, ConvertInvalidOffloadInfo) {
     AudioOffloadInfo invalid;
     audio_offload_info_t halInvalid = AUDIO_INFO_INITIALIZER;
-    halInvalid.channel_mask = AUDIO_CHANNEL_INVALID;
+    halInvalid.channel_mask = kInvalidHalChannelMask;
     halInvalid.format = kInvalidHalFormat;
     EXPECT_EQ(BAD_VALUE, HidlUtils::audioOffloadInfoFromHal(halInvalid, &invalid));
     invalid.base.channelMask = "random string";
@@ -575,7 +784,7 @@
 TEST(HidlUtils, ConvertInvalidConfig) {
     AudioConfig invalid;
     audio_config_t halInvalid = AUDIO_CONFIG_INITIALIZER;
-    halInvalid.channel_mask = AUDIO_CHANNEL_INVALID;
+    halInvalid.channel_mask = kInvalidHalChannelMask;
     halInvalid.format = kInvalidHalFormat;
     EXPECT_EQ(BAD_VALUE, HidlUtils::audioConfigFromHal(halInvalid, false /*isInput*/, &invalid));
     EXPECT_EQ(BAD_VALUE, HidlUtils::audioConfigFromHal(halInvalid, true /*isInput*/, &invalid));
@@ -655,18 +864,18 @@
     halInvalid.type = AUDIO_PORT_TYPE_MIX;
     halInvalid.role = AUDIO_PORT_ROLE_NONE;  // note: this is valid.
     halInvalid.config_mask = AUDIO_PORT_CONFIG_CHANNEL_MASK;
-    halInvalid.channel_mask = AUDIO_CHANNEL_INVALID;
+    halInvalid.channel_mask = kInvalidHalChannelMask;
     EXPECT_EQ(BAD_VALUE, HidlUtils::audioPortConfigFromHal(halInvalid, &invalid));
-    invalid.base.channelMask = "random string";
+    invalid.base.channelMask.value("random string");
     EXPECT_EQ(BAD_VALUE, HidlUtils::audioPortConfigToHal(invalid, &halInvalid));
 }
 
 TEST(HidlUtils, ConvertAudioPortConfig) {
     AudioPortConfig config = {};
     config.id = 42;
-    config.base.sampleRateHz = 44100;
-    config.base.channelMask = toString(xsd::AudioChannelMask::AUDIO_CHANNEL_OUT_STEREO);
-    config.base.format = toString(xsd::AudioFormat::AUDIO_FORMAT_PCM_16_BIT);
+    config.base.sampleRateHz.value(44100);
+    config.base.channelMask.value(toString(xsd::AudioChannelMask::AUDIO_CHANNEL_OUT_STEREO));
+    config.base.format.value(toString(xsd::AudioFormat::AUDIO_FORMAT_PCM_16_BIT));
     config.gain.config({});
     config.gain.config().channelMask = toString(xsd::AudioChannelMask::AUDIO_CHANNEL_OUT_STEREO);
     config.ext.device({});
@@ -734,7 +943,7 @@
             {std::string(AUDIO_ATTRIBUTES_TAGS_MAX_SIZE - 1, HidlUtils::sAudioTagSeparator)}};
     EXPECT_EQ(BAD_VALUE, HidlUtils::audioTagsToHal(tagSeparator, halTag));
 
-    hidl_vec<AudioTag> notExtensions = {{"random string", "VX_", "VX_GOOGLE_$$"}};
+    hidl_vec<AudioTag> notExtensions = {{"", "random string", "VX_", "VX_GOOGLE_$$"}};
     EXPECT_EQ(BAD_VALUE, HidlUtils::audioTagsToHal(notExtensions, halTag));
 }
 
diff --git a/audio/core/all-versions/default/Stream.cpp b/audio/core/all-versions/default/Stream.cpp
index f964cbb..3f8efd2 100644
--- a/audio/core/all-versions/default/Stream.cpp
+++ b/audio/core/all-versions/default/Stream.cpp
@@ -278,23 +278,36 @@
     return Void();
 }
 
-Return<Result> Stream::setAudioProperties(const AudioConfigBase& config) {
-    audio_config_base_t halConfigBase = {};
-    status_t status = HidlUtils::audioConfigBaseToHal(config, &halConfigBase);
+Return<Result> Stream::setAudioProperties(const AudioConfigBaseOptional& config) {
+    audio_config_base_t halConfigBase = AUDIO_CONFIG_BASE_INITIALIZER;
+    bool formatSpecified, sRateSpecified, channelMaskSpecified;
+    status_t status = HidlUtils::audioConfigBaseOptionalToHal(
+            config, &halConfigBase, &formatSpecified, &sRateSpecified, &channelMaskSpecified);
     if (status != NO_ERROR) {
         return Stream::analyzeStatus("set_audio_properties", status);
     }
-    if (Result result = setParam(AudioParameter::keySamplingRate,
-                                 static_cast<int>(halConfigBase.sample_rate));
-        result != Result::OK) {
-        return result;
+    if (sRateSpecified) {
+        if (Result result = setParam(AudioParameter::keySamplingRate,
+                                     static_cast<int>(halConfigBase.sample_rate));
+            result != Result::OK) {
+            return result;
+        }
     }
-    if (Result result =
-                setParam(AudioParameter::keyChannels, static_cast<int>(halConfigBase.channel_mask));
-        result != Result::OK) {
-        return result;
+    if (channelMaskSpecified) {
+        if (Result result = setParam(AudioParameter::keyChannels,
+                                     static_cast<int>(halConfigBase.channel_mask));
+            result != Result::OK) {
+            return result;
+        }
     }
-    return setParam(AudioParameter::keyFormat, static_cast<int>(halConfigBase.format));
+    if (formatSpecified) {
+        if (Result result =
+                    setParam(AudioParameter::keyFormat, static_cast<int>(halConfigBase.format));
+            result != Result::OK) {
+            return result;
+        }
+    }
+    return Result::OK;
 }
 
 #endif  // MAJOR_VERSION <= 6
diff --git a/audio/core/all-versions/default/StreamIn.cpp b/audio/core/all-versions/default/StreamIn.cpp
index 2c5e9f1..c670a4d 100644
--- a/audio/core/all-versions/default/StreamIn.cpp
+++ b/audio/core/all-versions/default/StreamIn.cpp
@@ -233,7 +233,7 @@
     return mStreamCommon->getSupportedProfiles(_hidl_cb);
 }
 
-Return<Result> StreamIn::setAudioProperties(const AudioConfigBase& config) {
+Return<Result> StreamIn::setAudioProperties(const AudioConfigBaseOptional& config) {
     return mStreamCommon->setAudioProperties(config);
 }
 
diff --git a/audio/core/all-versions/default/StreamOut.cpp b/audio/core/all-versions/default/StreamOut.cpp
index ffd3b6b..0b9af24 100644
--- a/audio/core/all-versions/default/StreamOut.cpp
+++ b/audio/core/all-versions/default/StreamOut.cpp
@@ -239,7 +239,7 @@
     return mStreamCommon->getSupportedProfiles(_hidl_cb);
 }
 
-Return<Result> StreamOut::setAudioProperties(const AudioConfigBase& config) {
+Return<Result> StreamOut::setAudioProperties(const AudioConfigBaseOptional& config) {
     return mStreamCommon->setAudioProperties(config);
 }
 
diff --git a/audio/core/all-versions/default/include/core/default/Stream.h b/audio/core/all-versions/default/include/core/default/Stream.h
index 0865992..66d60e3 100644
--- a/audio/core/all-versions/default/include/core/default/Stream.h
+++ b/audio/core/all-versions/default/include/core/default/Stream.h
@@ -77,7 +77,7 @@
     Return<Result> setFormat(AudioFormat format) override;
 #else
     Return<void> getSupportedProfiles(getSupportedProfiles_cb _hidl_cb) override;
-    Return<Result> setAudioProperties(const AudioConfigBase& config) override;
+    Return<Result> setAudioProperties(const AudioConfigBaseOptional& config) override;
 #endif  // MAJOR_VERSION <= 6
     Return<void> getAudioProperties(getAudioProperties_cb _hidl_cb) override;
     Return<Result> addEffect(uint64_t effectId) override;
diff --git a/audio/core/all-versions/default/include/core/default/StreamIn.h b/audio/core/all-versions/default/include/core/default/StreamIn.h
index 651b3a6..a980f3f 100644
--- a/audio/core/all-versions/default/include/core/default/StreamIn.h
+++ b/audio/core/all-versions/default/include/core/default/StreamIn.h
@@ -72,7 +72,7 @@
     Return<Result> setFormat(AudioFormat format) override;
 #else
     Return<void> getSupportedProfiles(getSupportedProfiles_cb _hidl_cb) override;
-    Return<Result> setAudioProperties(const AudioConfigBase& config) override;
+    Return<Result> setAudioProperties(const AudioConfigBaseOptional& config) override;
 #endif  // MAJOR_VERSION <= 6
     Return<void> getAudioProperties(getAudioProperties_cb _hidl_cb) override;
     Return<Result> addEffect(uint64_t effectId) override;
diff --git a/audio/core/all-versions/default/include/core/default/StreamOut.h b/audio/core/all-versions/default/include/core/default/StreamOut.h
index b8e8515..ccc1c1a 100644
--- a/audio/core/all-versions/default/include/core/default/StreamOut.h
+++ b/audio/core/all-versions/default/include/core/default/StreamOut.h
@@ -72,7 +72,7 @@
     Return<Result> setFormat(AudioFormat format) override;
 #else
     Return<void> getSupportedProfiles(getSupportedProfiles_cb _hidl_cb) override;
-    Return<Result> setAudioProperties(const AudioConfigBase& config) override;
+    Return<Result> setAudioProperties(const AudioConfigBaseOptional& config) override;
 #endif  // MAJOR_VERSION <= 6
     Return<void> getAudioProperties(getAudioProperties_cb _hidl_cb) override;
     Return<Result> addEffect(uint64_t effectId) override;
diff --git a/audio/core/all-versions/vts/functional/7.0/AudioPrimaryHidlHalTest.cpp b/audio/core/all-versions/vts/functional/7.0/AudioPrimaryHidlHalTest.cpp
index 7fca610..be1ffbb 100644
--- a/audio/core/all-versions/vts/functional/7.0/AudioPrimaryHidlHalTest.cpp
+++ b/audio/core/all-versions/vts/functional/7.0/AudioPrimaryHidlHalTest.cpp
@@ -367,10 +367,10 @@
     static std::vector<AudioPortConfig> invalids = [&] {
         std::vector<AudioPortConfig> result;
         AudioPortConfig invalidBaseChannelMask = valids[PORT_CONF_MINIMAL];
-        invalidBaseChannelMask.base.channelMask = "random_string";
+        invalidBaseChannelMask.base.channelMask.value("random_string");
         result.push_back(std::move(invalidBaseChannelMask));
         AudioPortConfig invalidBaseFormat = valids[PORT_CONF_MINIMAL];
-        invalidBaseFormat.base.format = "random_string";
+        invalidBaseFormat.base.format.value("random_string");
         result.push_back(std::move(invalidBaseFormat));
         AudioPortConfig invalidGainMode = valids[PORT_CONF_WITH_GAIN];
         invalidGainMode.gain.config().mode = {{"random_string"}};
@@ -724,19 +724,19 @@
         areAudioPatchesSupported() ? doc::partialTest("Audio patches are supported")
                                    : testSetDevicesInvalidDeviceAddress(stream.get()));
 
-static void testSetAudioPropertiesInvalidArguments(IStream* stream, const AudioConfigBase& base) {
-    AudioConfigBase invalidFormat = base;
-    invalidFormat.format = "random_string";
+static void testSetAudioPropertiesInvalidArguments(IStream* stream) {
+    AudioConfigBaseOptional invalidFormat;
+    invalidFormat.format.value("random_string");
     ASSERT_RESULT(invalidArgsOrNotSupported, stream->setAudioProperties(invalidFormat));
 
-    AudioConfigBase invalidChannelMask = base;
-    invalidChannelMask.channelMask = "random_string";
+    AudioConfigBaseOptional invalidChannelMask;
+    invalidChannelMask.channelMask.value("random_string");
     ASSERT_RESULT(invalidArgsOrNotSupported, stream->setAudioProperties(invalidChannelMask));
 }
 TEST_SINGLE_CONFIG_IO_STREAM(
         SetAudioPropertiesInvalidArguments,
         "Verify that invalid arguments are rejected by IStream::setAudioProperties",
-        testSetAudioPropertiesInvalidArguments(stream.get(), audioConfig.base));
+        testSetAudioPropertiesInvalidArguments(stream.get()));
 
 TEST_P(SingleConfigOutputStreamTest, UpdateInvalidSourceMetadata) {
     doc::test("Verify that invalid metadata is rejected by IStreamOut::updateSourceMetadata");
diff --git a/audio/core/all-versions/vts/functional/AudioPrimaryHidlHalTest.h b/audio/core/all-versions/vts/functional/AudioPrimaryHidlHalTest.h
index f145b60..2b9e336 100644
--- a/audio/core/all-versions/vts/functional/AudioPrimaryHidlHalTest.h
+++ b/audio/core/all-versions/vts/functional/AudioPrimaryHidlHalTest.h
@@ -1155,13 +1155,14 @@
     for (const auto& profile : profiles) {
         for (const auto& sampleRate : profile.sampleRates) {
             for (const auto& channelMask : profile.channelMasks) {
-                AudioConfigBase config{.format = profile.format,
-                                       .sampleRateHz = sampleRate,
-                                       .channelMask = {{channelMask}}};
+                AudioConfigBaseOptional config;
+                config.format.value(profile.format);
+                config.sampleRateHz.value(sampleRate);
+                config.channelMask.value(channelMask);
                 auto ret = stream->setAudioProperties(config);
                 EXPECT_TRUE(ret.isOk());
-                EXPECT_EQ(Result::OK, ret) << config.format << "; " << config.sampleRateHz << "; "
-                                           << toString(config.channelMask);
+                EXPECT_EQ(Result::OK, ret)
+                        << profile.format << "; " << sampleRate << "; " << channelMask;
             }
         }
     }
@@ -1169,7 +1170,7 @@
 
 TEST_IO_STREAM(SetAudioProperties, "Call setAudioProperties for all supported profiles",
                testSetAudioProperties(stream.get()))
-#endif
+#endif  // MAJOR_VERSION <= 6
 
 static void testGetAudioProperties(IStream* stream, AudioConfig expectedConfig) {
 #if MAJOR_VERSION <= 6
diff --git a/audio/effect/7.0/types.hal b/audio/effect/7.0/types.hal
index c4cb213..bb2d7b3 100644
--- a/audio/effect/7.0/types.hal
+++ b/audio/effect/7.0/types.hal
@@ -17,6 +17,7 @@
 package android.hardware.audio.effect@7.0;
 
 import android.hardware.audio.common@7.0;
+import android.hidl.safe_union@1.0;
 
 enum Result : int32_t {
     OK,
@@ -248,32 +249,19 @@
 };
 
 /**
- * Determines what fields of EffectBufferConfig need to be considered.
- */
-@export(name="", value_prefix="EFFECT_CONFIG_")
-enum EffectConfigParameters : int32_t {
-    /** Buffer field. */
-    BUFFER = 0x0001,
-    /** Sampling rate. */
-    SMP_RATE = 0x0002,
-    /** Channels. */
-    CHANNELS = 0x0004,
-    /** Format. */
-    FORMAT = 0x0008,
-    /** Access mode. */
-    ACC_MODE = 0x0010,
-    // Note that the 2.0 ALL have been moved to an helper function
-};
-
-/**
  * The buffer config structure specifies the input or output audio format
  * to be used by the effect engine.
  */
 struct EffectBufferConfig {
-    AudioBuffer buffer;
-    AudioConfigBase base;
-    EffectBufferAccess accessMode;
-    bitfield<EffectConfigParameters> mask;
+    safe_union OptionalBuffer {
+        Monostate unspecified;
+        AudioBuffer buf;
+    } buffer;
+    AudioConfigBaseOptional base;
+    safe_union OptionalAccessMode {
+        Monostate unspecified;
+        EffectBufferAccess value;
+    } accessMode;
 };
 
 struct EffectConfig {
diff --git a/audio/effect/all-versions/default/Effect.cpp b/audio/effect/all-versions/default/Effect.cpp
index edd364c..58f1779 100644
--- a/audio/effect/all-versions/default/Effect.cpp
+++ b/audio/effect/all-versions/default/Effect.cpp
@@ -249,14 +249,17 @@
 
 void Effect::effectBufferConfigFromHal(const buffer_config_t& halConfig,
                                        EffectBufferConfig* config) {
-    config->buffer.id = 0;
-    config->buffer.frameCount = 0;
+    config->buffer.unspecified();
     audio_config_base_t halConfigBase = {halConfig.samplingRate,
                                          static_cast<audio_channel_mask_t>(halConfig.channels),
                                          static_cast<audio_format_t>(halConfig.format)};
-    (void)HidlUtils::audioConfigBaseFromHal(halConfigBase, mIsInput, &config->base);
-    config->accessMode = EffectBufferAccess(halConfig.accessMode);
-    config->mask = static_cast<decltype(config->mask)>(halConfig.mask);
+    (void)HidlUtils::audioConfigBaseOptionalFromHal(
+            halConfigBase, mIsInput, halConfig.mask & EFFECT_CONFIG_FORMAT,
+            halConfig.mask & EFFECT_CONFIG_SMP_RATE, halConfig.mask & EFFECT_CONFIG_CHANNELS,
+            &config->base);
+    if (halConfig.mask & EFFECT_CONFIG_ACC_MODE) {
+        config->accessMode.value(EffectBufferAccess(halConfig.accessMode));
+    }
 }
 
 // static
@@ -265,17 +268,32 @@
     // using 'setProcessBuffers'.
     halConfig->buffer.frameCount = 0;
     halConfig->buffer.raw = nullptr;
-    audio_config_base_t halConfigBase;
-    (void)HidlUtils::audioConfigBaseToHal(config.base, &halConfigBase);
-    halConfig->samplingRate = halConfigBase.sample_rate;
-    halConfig->channels = halConfigBase.channel_mask;
-    halConfig->format = halConfigBase.format;
+    audio_config_base_t halConfigBase = AUDIO_CONFIG_BASE_INITIALIZER;
+    bool formatSpecified = false, sRateSpecified = false, channelMaskSpecified = false;
+    (void)HidlUtils::audioConfigBaseOptionalToHal(config.base, &halConfigBase, &formatSpecified,
+                                                  &sRateSpecified, &channelMaskSpecified);
+    halConfig->mask = 0;
+    if (sRateSpecified) {
+        halConfig->mask |= EFFECT_CONFIG_SMP_RATE;
+        halConfig->samplingRate = halConfigBase.sample_rate;
+    }
+    if (channelMaskSpecified) {
+        halConfig->mask |= EFFECT_CONFIG_CHANNELS;
+        halConfig->channels = halConfigBase.channel_mask;
+    }
+    if (formatSpecified) {
+        halConfig->mask |= EFFECT_CONFIG_FORMAT;
+        halConfig->format = halConfigBase.format;
+    }
     // Note: The framework code does not use BP.
     halConfig->bufferProvider.cookie = nullptr;
     halConfig->bufferProvider.getBuffer = nullptr;
     halConfig->bufferProvider.releaseBuffer = nullptr;
-    halConfig->accessMode = static_cast<uint8_t>(config.accessMode);
-    halConfig->mask = static_cast<uint8_t>(config.mask);
+    if (config.accessMode.getDiscriminator() ==
+        EffectBufferConfig::OptionalAccessMode::hidl_discriminator::value) {
+        halConfig->mask |= EFFECT_CONFIG_ACC_MODE;
+        halConfig->accessMode = static_cast<uint8_t>(config.accessMode.value());
+    }
 }
 
 #endif  // MAJOR_VERSION <= 6
diff --git a/audio/effect/all-versions/vts/functional/VtsHalAudioEffectTargetTest.cpp b/audio/effect/all-versions/vts/functional/VtsHalAudioEffectTargetTest.cpp
index 35ff869..15a2fd9 100644
--- a/audio/effect/all-versions/vts/functional/VtsHalAudioEffectTargetTest.cpp
+++ b/audio/effect/all-versions/vts/functional/VtsHalAudioEffectTargetTest.cpp
@@ -264,8 +264,10 @@
     *channelCount = audio_channel_count_from_out_mask(
         static_cast<audio_channel_mask_t>(currentConfig.outputCfg.channels));
 #else
+    ASSERT_EQ(AudioConfigBaseOptional::ChannelMask::hidl_discriminator::value,
+              currentConfig.outputCfg.base.channelMask.getDiscriminator());
     *channelCount = android::audio::policy::configuration::V7_0::getChannelCount(
-            currentConfig.outputCfg.base.channelMask);
+            currentConfig.outputCfg.base.channelMask.value());
     ASSERT_NE(*channelCount, 0);
 #endif
 }
@@ -315,10 +317,10 @@
 std::vector<EffectBufferConfig> generateInvalidConfigs(const EffectBufferConfig& src) {
     std::vector<EffectBufferConfig> result;
     EffectBufferConfig invalidFormat = src;
-    invalidFormat.base.format = "random_string";
+    invalidFormat.base.format.value("random_string");
     result.push_back(std::move(invalidFormat));
     EffectBufferConfig invalidChannelMask = src;
-    invalidChannelMask.base.channelMask = "random_string";
+    invalidChannelMask.base.channelMask.value("random_string");
     result.push_back(std::move(invalidChannelMask));
     return result;
 }
@@ -395,17 +397,22 @@
            rhs.data.handle() == nullptr;
 }
 
+#if MAJOR_VERSION <= 6
 inline bool operator==(const EffectBufferConfig& lhs, const EffectBufferConfig& rhs) {
     return lhs.buffer == rhs.buffer &&
-#if MAJOR_VERSION <= 6
            lhs.samplingRateHz == rhs.samplingRateHz && lhs.channels == rhs.channels &&
            lhs.format == rhs.format &&
-#else
-           lhs.base.sampleRateHz == rhs.base.sampleRateHz &&
-           lhs.base.channelMask == rhs.base.channelMask && lhs.base.format == rhs.base.format &&
-#endif
            lhs.accessMode == rhs.accessMode && lhs.mask == rhs.mask;
 }
+#else
+inline bool operator==(const EffectBufferConfig& lhs, const EffectBufferConfig& rhs) {
+    return lhs.buffer.getDiscriminator() == rhs.buffer.getDiscriminator() &&
+           (lhs.buffer.getDiscriminator() ==
+                    EffectBufferConfig::OptionalBuffer::hidl_discriminator::unspecified ||
+            lhs.buffer.buf() == rhs.buffer.buf()) &&
+           lhs.base == rhs.base && lhs.accessMode == rhs.accessMode;
+}
+#endif  // MAJOR_VERSION <= 6
 
 inline bool operator==(const EffectConfig& lhs, const EffectConfig& rhs) {
     return lhs.inputCfg == rhs.inputCfg && lhs.outputCfg == rhs.outputCfg;