Merge pull request #643 from google/gbg/auracast-audio-io

auracast audio io
2026-05-08 03:58:01 +00:00 · 2025-02-08 18:19:24 -05:00
parent c02c1f33d2 859bb0609f
commit 3f6f036270
27 changed files with 1388 additions and 414 deletions
--- a/bumble/audio/init.py
+++ b/bumble/audio/init.py
@@ -0,0 +1,17 @@
+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# -----------------------------------------------------------------------------
+# Imports
+# -----------------------------------------------------------------------------
--- a/bumble/audio/io.py
+++ b/bumble/audio/io.py
@@ -0,0 +1,553 @@
+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# -----------------------------------------------------------------------------
+# Imports
+# -----------------------------------------------------------------------------
+from __future__ import annotations
+
+import asyncio
+import abc
+from concurrent.futures import ThreadPoolExecutor
+import dataclasses
+import enum
+import logging
+import pathlib
+from typing import (
+    AsyncGenerator,
+    BinaryIO,
+    TYPE_CHECKING,
+)
+import sys
+import wave
+
+from bumble.colors import color
+
+if TYPE_CHECKING:
+    import sounddevice  # type: ignore[import-untyped]
+
+
+# -----------------------------------------------------------------------------
+# Logging
+# -----------------------------------------------------------------------------
+logger = logging.getLogger(__name__)
+
+
+# -----------------------------------------------------------------------------
+# Classes
+# -----------------------------------------------------------------------------
+@dataclasses.dataclass
+class PcmFormat:
+    class Endianness(enum.Enum):
+        LITTLE = 0
+        BIG = 1
+
+    class SampleType(enum.Enum):
+        FLOAT32 = 0
+        INT16 = 1
+
+    endianness: Endianness
+    sample_type: SampleType
+    sample_rate: int
+    channels: int
+
+    @classmethod
+    def from_str(cls, format_str: str) -> PcmFormat:
+        endianness = cls.Endianness.LITTLE  # Others not yet supported.
+        sample_type_str, sample_rate_str, channels_str = format_str.split(',')
+        if sample_type_str == 'int16le':
+            sample_type = cls.SampleType.INT16
+        elif sample_type_str == 'float32le':
+            sample_type = cls.SampleType.FLOAT32
+        else:
+            raise ValueError(f'sample type {sample_type_str} not supported')
+        sample_rate = int(sample_rate_str)
+        channels = int(channels_str)
+
+        return cls(endianness, sample_type, sample_rate, channels)
+
+    @property
+    def bytes_per_sample(self) -> int:
+        return 2 if self.sample_type == self.SampleType.INT16 else 4
+
+
+def check_audio_output(output: str) -> bool:
+    if output == 'device' or output.startswith('device:'):
+        try:
+            import sounddevice
+        except ImportError as exc:
+            raise ValueError(
+                'audio output not available (sounddevice python module not installed)'
+            ) from exc
+        except OSError as exc:
+            raise ValueError(
+                'audio output not available '
+                '(sounddevice python module failed to load: '
+                f'{exc})'
+            ) from exc
+
+        if output == 'device':
+            # Default device
+            return True
+
+        # Specific device
+        device = output[7:]
+        if device == '?':
+            print(color('Audio Devices:', 'yellow'))
+            for device_info in [
+                device_info
+                for device_info in sounddevice.query_devices()
+                if device_info['max_output_channels'] > 0
+            ]:
+                device_index = device_info['index']
+                is_default = (
+                    color(' [default]', 'green')
+                    if sounddevice.default.device[1] == device_index
+                    else ''
+                )
+                print(
+                    f'{color(device_index, "cyan")}: {device_info["name"]}{is_default}'
+                )
+            return False
+
+        try:
+            device_info = sounddevice.query_devices(int(device))
+        except sounddevice.PortAudioError as exc:
+            raise ValueError('No such audio device') from exc
+
+        if device_info['max_output_channels'] < 1:
+            raise ValueError(
+                f'Device {device} ({device_info["name"]}) does not have an output'
+            )
+
+    return True
+
+
+async def create_audio_output(output: str) -> AudioOutput:
+    if output == 'stdout':
+        return StreamAudioOutput(sys.stdout.buffer)
+
+    if output == 'device' or output.startswith('device:'):
+        device_name = '' if output == 'device' else output[7:]
+        return SoundDeviceAudioOutput(device_name)
+
+    if output == 'ffplay':
+        return SubprocessAudioOutput(
+            command=(
+                'ffplay -probesize 32 -fflags nobuffer -analyzeduration 0 '
+                '-ar {sample_rate} '
+                '-ch_layout {channel_layout} '
+                '-f f32le pipe:0'
+            )
+        )
+
+    if output.startswith('file:'):
+        return FileAudioOutput(output[5:])
+
+    raise ValueError('unsupported audio output')
+
+
+class AudioOutput(abc.ABC):
+    """Audio output to which PCM samples can be written."""
+
+    async def open(self, pcm_format: PcmFormat) -> None:
+        """Start the output."""
+
+    @abc.abstractmethod
+    def write(self, pcm_samples: bytes) -> None:
+        """Write PCM samples. Must not block."""
+
+    async def aclose(self) -> None:
+        """Close the output."""
+
+
+class ThreadedAudioOutput(AudioOutput):
+    """Base class for AudioOutput classes that may need to call blocking functions.
+
+    The actual writing is performed in a thread, so as to ensure that calling write()
+    does not block the caller.
+    """
+
+    def __init__(self) -> None:
+        self._thread_pool = ThreadPoolExecutor(1)
+        self._pcm_samples: asyncio.Queue[bytes] = asyncio.Queue()
+        self._write_task = asyncio.create_task(self._write_loop())
+
+    async def _write_loop(self) -> None:
+        while True:
+            pcm_samples = await self._pcm_samples.get()
+            await asyncio.get_running_loop().run_in_executor(
+                self._thread_pool, self._write, pcm_samples
+            )
+
+    @abc.abstractmethod
+    def _write(self, pcm_samples: bytes) -> None:
+        """This method does the actual writing and can block."""
+
+    def write(self, pcm_samples: bytes) -> None:
+        self._pcm_samples.put_nowait(pcm_samples)
+
+    def _close(self) -> None:
+        """This method does the actual closing and can block."""
+
+    async def aclose(self) -> None:
+        await asyncio.get_running_loop().run_in_executor(self._thread_pool, self._close)
+        self._write_task.cancel()
+        self._thread_pool.shutdown()
+
+
+class SoundDeviceAudioOutput(ThreadedAudioOutput):
+    def __init__(self, device_name: str) -> None:
+        super().__init__()
+        self._device = int(device_name) if device_name else None
+        self._stream: sounddevice.RawOutputStream | None = None
+
+    async def open(self, pcm_format: PcmFormat) -> None:
+        import sounddevice  # pylint: disable=import-error
+
+        self._stream = sounddevice.RawOutputStream(
+            samplerate=pcm_format.sample_rate,
+            device=self._device,
+            channels=pcm_format.channels,
+            dtype='float32',
+        )
+        self._stream.start()
+
+    def _write(self, pcm_samples: bytes) -> None:
+        if self._stream is None:
+            return
+
+        try:
+            self._stream.write(pcm_samples)
+        except Exception as error:
+            print(f'Sound device error: {error}')
+            raise
+
+    def _close(self):
+        self._stream.stop()
+        self._stream = None
+
+
+class StreamAudioOutput(ThreadedAudioOutput):
+    """AudioOutput where PCM samples are written to a stream that may block."""
+
+    def __init__(self, stream: BinaryIO) -> None:
+        super().__init__()
+        self._stream = stream
+
+    def _write(self, pcm_samples: bytes) -> None:
+        self._stream.write(pcm_samples)
+        self._stream.flush()
+
+
+class FileAudioOutput(StreamAudioOutput):
+    """AudioOutput where PCM samples are written to a file."""
+
+    def __init__(self, filename: str) -> None:
+        self._file = open(filename, "wb")
+        super().__init__(self._file)
+
+    async def shutdown(self):
+        self._file.close()
+        return await super().shutdown()
+
+
+class SubprocessAudioOutput(AudioOutput):
+    """AudioOutput where audio samples are written to a subprocess via stdin."""
+
+    def __init__(self, command: str) -> None:
+        self._command = command
+        self._subprocess: asyncio.subprocess.Process | None
+
+    async def open(self, pcm_format: PcmFormat) -> None:
+        if pcm_format.channels == 1:
+            channel_layout = 'mono'
+        elif pcm_format.channels == 2:
+            channel_layout = 'stereo'
+        else:
+            raise ValueError(f'{pcm_format.channels} channels not supported')
+
+        command = self._command.format(
+            sample_rate=pcm_format.sample_rate, channel_layout=channel_layout
+        )
+        self._subprocess = await asyncio.create_subprocess_shell(
+            command,
+            stdin=asyncio.subprocess.PIPE,
+            stdout=asyncio.subprocess.PIPE,
+            stderr=asyncio.subprocess.PIPE,
+        )
+
+    def write(self, pcm_samples: bytes) -> None:
+        if self._subprocess is None or self._subprocess.stdin is None:
+            return
+
+        self._subprocess.stdin.write(pcm_samples)
+
+    async def aclose(self):
+        if self._subprocess:
+            self._subprocess.terminate()
+
+
+def check_audio_input(input: str) -> bool:
+    if input == 'device' or input.startswith('device:'):
+        try:
+            import sounddevice  # pylint: disable=import-error
+        except ImportError as exc:
+            raise ValueError(
+                'audio input not available (sounddevice python module not installed)'
+            ) from exc
+        except OSError as exc:
+            raise ValueError(
+                'audio input not available '
+                '(sounddevice python module failed to load: '
+                f'{exc})'
+            ) from exc
+
+        if input == 'device':
+            # Default device
+            return True
+
+        # Specific device
+        device = input[7:]
+        if device == '?':
+            print(color('Audio Devices:', 'yellow'))
+            for device_info in [
+                device_info
+                for device_info in sounddevice.query_devices()
+                if device_info['max_input_channels'] > 0
+            ]:
+                device_index = device_info["index"]
+                is_mono = device_info['max_input_channels'] == 1
+                max_channels = color(f'[{"mono" if is_mono else "stereo"}]', 'cyan')
+                is_default = (
+                    color(' [default]', 'green')
+                    if sounddevice.default.device[0] == device_index
+                    else ''
+                )
+                print(
+                    f'{color(device_index, "cyan")}: {device_info["name"]}'
+                    f' {max_channels}{is_default}'
+                )
+            return False
+
+        try:
+            device_info = sounddevice.query_devices(int(device))
+        except sounddevice.PortAudioError as exc:
+            raise ValueError('No such audio device') from exc
+
+        if device_info['max_input_channels'] < 1:
+            raise ValueError(
+                f'Device {device} ({device_info["name"]}) does not have an input'
+            )
+
+    return True
+
+
+async def create_audio_input(input: str, input_format: str) -> AudioInput:
+    pcm_format: PcmFormat | None
+    if input_format == 'auto':
+        pcm_format = None
+    else:
+        pcm_format = PcmFormat.from_str(input_format)
+
+    if input == 'stdin':
+        if not pcm_format:
+            raise ValueError('input format details required for stdin')
+        return StreamAudioInput(sys.stdin.buffer, pcm_format)
+
+    if input == 'device' or input.startswith('device:'):
+        if not pcm_format:
+            raise ValueError('input format details required for device')
+        device_name = '' if input == 'device' else input[7:]
+        return SoundDeviceAudioInput(device_name, pcm_format)
+
+    # If there's no file: prefix, check if we can assume it is a file.
+    if pathlib.Path(input).is_file():
+        input = 'file:' + input
+
+    if input.startswith('file:'):
+        filename = input[5:]
+        if filename.endswith('.wav'):
+            if input_format != 'auto':
+                raise ValueError(".wav file only supported with 'auto' format")
+            return WaveAudioInput(filename)
+
+        if pcm_format is None:
+            raise ValueError('input format details required for raw PCM files')
+        return FileAudioInput(filename, pcm_format)
+
+    raise ValueError('input not supported')
+
+
+class AudioInput(abc.ABC):
+    """Audio input that produces PCM samples."""
+
+    @abc.abstractmethod
+    async def open(self) -> PcmFormat:
+        """Open the input."""
+
+    @abc.abstractmethod
+    def frames(self, frame_size: int) -> AsyncGenerator[bytes]:
+        """Generate one frame of PCM samples. Must not block."""
+
+    async def aclose(self) -> None:
+        """Close the input."""
+
+
+class ThreadedAudioInput(AudioInput):
+    """Base class for AudioInput implementation where reading samples may block."""
+
+    def __init__(self) -> None:
+        self._thread_pool = ThreadPoolExecutor(1)
+        self._pcm_samples: asyncio.Queue[bytes] = asyncio.Queue()
+
+    @abc.abstractmethod
+    def _read(self, frame_size: int) -> bytes:
+        pass
+
+    @abc.abstractmethod
+    def _open(self) -> PcmFormat:
+        pass
+
+    def _close(self) -> None:
+        pass
+
+    async def open(self) -> PcmFormat:
+        return await asyncio.get_running_loop().run_in_executor(
+            self._thread_pool, self._open
+        )
+
+    async def frames(self, frame_size: int) -> AsyncGenerator[bytes]:
+        while pcm_sample := await asyncio.get_running_loop().run_in_executor(
+            self._thread_pool, self._read, frame_size
+        ):
+            yield pcm_sample
+
+    async def aclose(self) -> None:
+        await asyncio.get_running_loop().run_in_executor(self._thread_pool, self._close)
+        self._thread_pool.shutdown()
+
+
+class WaveAudioInput(ThreadedAudioInput):
+    """Audio input that reads PCM samples from a .wav file."""
+
+    def __init__(self, filename: str) -> None:
+        super().__init__()
+        self._filename = filename
+        self._wav: wave.Wave_read | None = None
+        self._bytes_read = 0
+
+    def _open(self) -> PcmFormat:
+        self._wav = wave.open(self._filename, 'rb')
+        if self._wav.getsampwidth() != 2:
+            raise ValueError('sample width not supported')
+        return PcmFormat(
+            PcmFormat.Endianness.LITTLE,
+            PcmFormat.SampleType.INT16,
+            self._wav.getframerate(),
+            self._wav.getnchannels(),
+        )
+
+    def _read(self, frame_size: int) -> bytes:
+        if not self._wav:
+            return b''
+
+        pcm_samples = self._wav.readframes(frame_size)
+        if not pcm_samples and self._bytes_read:
+            # Loop around.
+            self._wav.rewind()
+            self._bytes_read = 0
+            pcm_samples = self._wav.readframes(frame_size)
+
+        self._bytes_read += len(pcm_samples)
+        return pcm_samples
+
+    def _close(self) -> None:
+        if self._wav:
+            self._wav.close()
+
+
+class StreamAudioInput(ThreadedAudioInput):
+    """AudioInput where samples are read from a raw PCM stream that may block."""
+
+    def __init__(self, stream: BinaryIO, pcm_format: PcmFormat) -> None:
+        super().__init__()
+        self._stream = stream
+        self._pcm_format = pcm_format
+
+    def _open(self) -> PcmFormat:
+        return self._pcm_format
+
+    def _read(self, frame_size: int) -> bytes:
+        return self._stream.read(
+            frame_size * self._pcm_format.channels * self._pcm_format.bytes_per_sample
+        )
+
+
+class FileAudioInput(StreamAudioInput):
+    """AudioInput where PCM samples are read from a raw PCM file."""
+
+    def __init__(self, filename: str, pcm_format: PcmFormat) -> None:
+        self._stream = open(filename, "rb")
+        super().__init__(self._stream, pcm_format)
+
+    def _close(self) -> None:
+        self._stream.close()
+
+
+class SoundDeviceAudioInput(ThreadedAudioInput):
+    def __init__(self, device_name: str, pcm_format: PcmFormat) -> None:
+        super().__init__()
+        self._device = int(device_name) if device_name else None
+        self._pcm_format = pcm_format
+        self._stream: sounddevice.RawInputStream | None = None
+
+    def _open(self) -> PcmFormat:
+        import sounddevice  # pylint: disable=import-error
+
+        self._stream = sounddevice.RawInputStream(
+            samplerate=self._pcm_format.sample_rate,
+            device=self._device,
+            channels=self._pcm_format.channels,
+            dtype='int16',
+        )
+        self._stream.start()
+
+        return PcmFormat(
+            PcmFormat.Endianness.LITTLE,
+            PcmFormat.SampleType.INT16,
+            self._pcm_format.sample_rate,
+            2,
+        )
+
+    def _read(self, frame_size: int) -> bytes:
+        if not self._stream:
+            return b''
+        pcm_buffer, overflowed = self._stream.read(frame_size)
+        if overflowed:
+            logger.warning("input overflow")
+
+        # Convert the buffer to stereo if needed
+        if self._pcm_format.channels == 1:
+            stereo_buffer = bytearray()
+            for i in range(frame_size):
+                sample = pcm_buffer[i * 2 : i * 2 + 2]
+                stereo_buffer += sample + sample
+            return stereo_buffer
+
+        return bytes(pcm_buffer)
+
+    def _close(self):
+        self._stream.stop()
+        self._stream = None
--- a/bumble/device.py
+++ b/bumble/device.py
@@ -17,6 +17,7 @@
 # -----------------------------------------------------------------------------
 from __future__ import annotations
 import asyncio
+import collections
 from collections.abc import Iterable, Sequence
 from contextlib import (
    asynccontextmanager,
@@ -36,6 +37,7 @@ from typing import (
    Any,
    Callable,
    ClassVar,
+    Deque,
    Dict,
    Optional,
    Type,
@@ -1506,6 +1508,49 @@ class BisLink(_IsoLink):
        self.device = self.big.device


+# -----------------------------------------------------------------------------
+class IsoPacketStream:
+    """Async stream that can write SDUs to a CIS or BIS, with a maximum queue size."""
+
+    iso_link: _IsoLink
+    data_packet_queue: DataPacketQueue
+
+    def __init__(self, iso_link: _IsoLink, max_queue_size: int) -> None:
+        if iso_link.data_packet_queue is None:
+            raise ValueError('link has no data packet queue')
+
+        self.iso_link = iso_link
+        self.data_packet_queue = iso_link.data_packet_queue
+        self.data_packet_queue.on('flow', self._on_flow)
+        self._thresholds: Deque[int] = collections.deque()
+        self._semaphore = asyncio.Semaphore(max_queue_size)
+
+    def _on_flow(self) -> None:
+        # Release the semaphore once for each completed packet.
+        while (
+            self._thresholds and self.data_packet_queue.completed >= self._thresholds[0]
+        ):
+            self._thresholds.popleft()
+            self._semaphore.release()
+
+    async def write(self, sdu: bytes) -> None:
+        """
+        Write an SDU to the queue.
+
+        This method blocks until there are fewer than max_queue_size packets queued
+        but not yet completed.
+        """
+
+        # Wait until there's space in the queue.
+        await self._semaphore.acquire()
+
+        # Queue the packet.
+        self.iso_link.write(sdu)
+
+        # Remember the position of the packet so we can know when it is completed.
+        self._thresholds.append(self.data_packet_queue.queued)
+
+
 # -----------------------------------------------------------------------------
 class Connection(CompositeEventEmitter):
    device: Device
--- a/bumble/gatt.py
+++ b/bumble/gatt.py
@@ -42,7 +42,7 @@ from typing import (
 )

 from bumble.colors import color
-from bumble.core import BaseBumbleError, UUID
+from bumble.core import BaseBumbleError, InvalidOperationError, UUID
 from bumble.att import Attribute, AttributeValue
 from bumble.utils import ByteSerializable

@@ -314,6 +314,7 @@ GATT_CENTRAL_ADDRESS_RESOLUTION__CHARACTERISTIC                = UUID.from_16_bi
 GATT_CLIENT_SUPPORTED_FEATURES_CHARACTERISTIC                  = UUID.from_16_bits(0x2B29, 'Client Supported Features')
 GATT_DATABASE_HASH_CHARACTERISTIC                              = UUID.from_16_bits(0x2B2A, 'Database Hash')
 GATT_SERVER_SUPPORTED_FEATURES_CHARACTERISTIC                  = UUID.from_16_bits(0x2B3A, 'Server Supported Features')
+GATT_LE_GATT_SECURITY_LEVELS_CHARACTERISTIC                    = UUID.from_16_bits(0x2BF5, 'E GATT Security Levels')

 # fmt: on
 # pylint: enable=line-too-long
@@ -322,8 +323,6 @@ GATT_SERVER_SUPPORTED_FEATURES_CHARACTERISTIC                  = UUID.from_16_bi
 # -----------------------------------------------------------------------------
 # Utils
 # -----------------------------------------------------------------------------
-
-
 def show_services(services: Iterable[Service]) -> None:
    for service in services:
        print(color(str(service), 'cyan'))
@@ -679,10 +678,14 @@ class DelegatedCharacteristicAdapter(CharacteristicAdapter):
        self.decode = decode

    def encode_value(self, value):
-        return self.encode(value) if self.encode else value
+        if self.encode is None:
+            raise InvalidOperationError('delegated adapter does not have an encoder')
+        return self.encode(value)

    def decode_value(self, value):
-        return self.decode(value) if self.decode else value
+        if self.decode is None:
+            raise InvalidOperationError('delegate adapter does not have a decoder')
+        return self.decode(value)


 # -----------------------------------------------------------------------------
--- a/bumble/gatt_client.py
+++ b/bumble/gatt_client.py
@@ -78,6 +78,7 @@ from .gatt import (
    GATT_INCLUDE_ATTRIBUTE_TYPE,
    Characteristic,
    ClientCharacteristicConfigurationBits,
+    InvalidServiceError,
    TemplateService,
 )

@@ -162,12 +163,23 @@ class ServiceProxy(AttributeProxy):
        self.uuid = uuid
        self.characteristics = []

-    async def discover_characteristics(self, uuids=()):
+    async def discover_characteristics(self, uuids=()) -> list[CharacteristicProxy]:
        return await self.client.discover_characteristics(uuids, self)

-    def get_characteristics_by_uuid(self, uuid):
+    def get_characteristics_by_uuid(self, uuid: UUID) -> list[CharacteristicProxy]:
+        """Get all the characteristics with a specified UUID."""
        return self.client.get_characteristics_by_uuid(uuid, self)

+    def get_required_characteristic_by_uuid(self, uuid: UUID) -> CharacteristicProxy:
+        """
+        Get the first characteristic with a specified UUID.
+
+        If no characteristic with that UUID is found, an InvalidServiceError is raised.
+        """
+        if not (characteristics := self.get_characteristics_by_uuid(uuid)):
+            raise InvalidServiceError(f'{uuid} characteristic not found')
+        return characteristics[0]
+
    def __str__(self) -> str:
        return f'Service(handle=0x{self.handle:04X}, uuid={self.uuid})'

--- a/bumble/profiles/aics.py
+++ b/bumble/profiles/aics.py
@@ -451,54 +451,35 @@ class AICSServiceProxy(ProfileServiceProxy):
    def __init__(self, service_proxy: ServiceProxy) -> None:
        self.service_proxy = service_proxy

-        if not (
-            characteristics := service_proxy.get_characteristics_by_uuid(
-                GATT_AUDIO_INPUT_STATE_CHARACTERISTIC
-            )
-        ):
-            raise gatt.InvalidServiceError("Audio Input State Characteristic not found")
        self.audio_input_state = SerializableCharacteristicAdapter(
-            characteristics[0], AudioInputState
+            service_proxy.get_required_characteristic_by_uuid(
+                GATT_AUDIO_INPUT_STATE_CHARACTERISTIC
+            ),
+            AudioInputState,
        )

-        if not (
-            characteristics := service_proxy.get_characteristics_by_uuid(
-                GATT_GAIN_SETTINGS_ATTRIBUTE_CHARACTERISTIC
-            )
-        ):
-            raise gatt.InvalidServiceError(
-                "Gain Settings Attribute Characteristic not found"
-            )
        self.gain_settings_properties = SerializableCharacteristicAdapter(
-            characteristics[0], GainSettingsProperties
+            service_proxy.get_required_characteristic_by_uuid(
+                GATT_GAIN_SETTINGS_ATTRIBUTE_CHARACTERISTIC
+            ),
+            GainSettingsProperties,
        )

-        if not (
-            characteristics := service_proxy.get_characteristics_by_uuid(
+        self.audio_input_status = PackedCharacteristicAdapter(
+            service_proxy.get_required_characteristic_by_uuid(
                GATT_AUDIO_INPUT_STATUS_CHARACTERISTIC
-            )
-        ):
-            raise gatt.InvalidServiceError(
-                "Audio Input Status Characteristic not found"
-            )
-        self.audio_input_status = PackedCharacteristicAdapter(characteristics[0], 'B')
+            ),
+            'B',
+        )

-        if not (
-            characteristics := service_proxy.get_characteristics_by_uuid(
+        self.audio_input_control_point = (
+            service_proxy.get_required_characteristic_by_uuid(
                GATT_AUDIO_INPUT_CONTROL_POINT_CHARACTERISTIC
            )
-        ):
-            raise gatt.InvalidServiceError(
-                "Audio Input Control Point Characteristic not found"
-            )
-        self.audio_input_control_point = characteristics[0]
+        )

-        if not (
-            characteristics := service_proxy.get_characteristics_by_uuid(
+        self.audio_input_description = UTF8CharacteristicAdapter(
+            service_proxy.get_required_characteristic_by_uuid(
                GATT_AUDIO_INPUT_DESCRIPTION_CHARACTERISTIC
            )
-        ):
-            raise gatt.InvalidServiceError(
-                "Audio Input Description Characteristic not found"
-            )
-        self.audio_input_description = UTF8CharacteristicAdapter(characteristics[0])
+        )
--- a/bumble/profiles/asha.py
+++ b/bumble/profiles/asha.py
@@ -288,8 +288,8 @@ class AshaServiceProxy(gatt_client.ProfileServiceProxy):
                'psm_characteristic',
            ),
        ):
-            if not (
-                characteristics := self.service_proxy.get_characteristics_by_uuid(uuid)
-            ):
-                raise gatt.InvalidServiceError(f"Missing {uuid} Characteristic")
-            setattr(self, attribute_name, characteristics[0])
+            setattr(
+                self,
+                attribute_name,
+                self.service_proxy.get_required_characteristic_by_uuid(uuid),
+            )
--- a/bumble/profiles/bass.py
+++ b/bumble/profiles/bass.py
@@ -354,34 +354,25 @@ class BroadcastAudioScanServiceProxy(gatt_client.ProfileServiceProxy):
    SERVICE_CLASS = BroadcastAudioScanService

    broadcast_audio_scan_control_point: gatt_client.CharacteristicProxy
-    broadcast_receive_states: List[gatt.SerializableCharacteristicAdapter]
+    broadcast_receive_states: List[gatt.DelegatedCharacteristicAdapter]

    def __init__(self, service_proxy: gatt_client.ServiceProxy):
        self.service_proxy = service_proxy

-        if not (
-            characteristics := service_proxy.get_characteristics_by_uuid(
+        self.broadcast_audio_scan_control_point = (
+            service_proxy.get_required_characteristic_by_uuid(
                gatt.GATT_BROADCAST_AUDIO_SCAN_CONTROL_POINT_CHARACTERISTIC
            )
-        ):
-            raise gatt.InvalidServiceError(
-                "Broadcast Audio Scan Control Point characteristic not found"
-            )
-        self.broadcast_audio_scan_control_point = characteristics[0]
+        )

-        if not (
-            characteristics := service_proxy.get_characteristics_by_uuid(
+        self.broadcast_receive_states = [
+            gatt.DelegatedCharacteristicAdapter(
+                characteristic,
+                decode=lambda x: BroadcastReceiveState.from_bytes(x) if x else None,
+            )
+            for characteristic in service_proxy.get_characteristics_by_uuid(
                gatt.GATT_BROADCAST_RECEIVE_STATE_CHARACTERISTIC
            )
-        ):
-            raise gatt.InvalidServiceError(
-                "Broadcast Receive State characteristic not found"
-            )
-        self.broadcast_receive_states = [
-            gatt.SerializableCharacteristicAdapter(
-                characteristic, BroadcastReceiveState
-            )
-            for characteristic in characteristics
        ]

    async def send_control_point_operation(
--- a/bumble/profiles/gmap.py
+++ b/bumble/profiles/gmap.py
@@ -30,7 +30,6 @@ from bumble.gatt import (
    GATT_UGT_FEATURES_CHARACTERISTIC,
    GATT_BGS_FEATURES_CHARACTERISTIC,
    GATT_BGR_FEATURES_CHARACTERISTIC,
-    InvalidServiceError,
 )
 from bumble.gatt_client import ProfileServiceProxy, ServiceProxy
 from enum import IntFlag
@@ -154,14 +153,10 @@ class GamingAudioServiceProxy(ProfileServiceProxy):
    def __init__(self, service_proxy: ServiceProxy) -> None:
        self.service_proxy = service_proxy

-        if not (
-            characteristics := service_proxy.get_characteristics_by_uuid(
-                GATT_GMAP_ROLE_CHARACTERISTIC
-            )
-        ):
-            raise InvalidServiceError("GMAP Role Characteristic not found")
        self.gmap_role = DelegatedCharacteristicAdapter(
-            characteristic=characteristics[0],
+            service_proxy.get_required_characteristic_by_uuid(
+                GATT_GMAP_ROLE_CHARACTERISTIC
+            ),
            decode=lambda value: GmapRole(value[0]),
        )

--- a/bumble/profiles/le_audio.py
+++ b/bumble/profiles/le_audio.py
@@ -17,23 +17,35 @@
 # -----------------------------------------------------------------------------
 from __future__ import annotations
 import dataclasses
+import enum
 import struct
-from typing import List, Type
+from typing import Any, List, Type
 from typing_extensions import Self

+from bumble.profiles import bap
 from bumble import utils


 # -----------------------------------------------------------------------------
 # Classes
 # -----------------------------------------------------------------------------
+class AudioActiveState(utils.OpenIntEnum):
+    NO_AUDIO_DATA_TRANSMITTED = 0x00
+    AUDIO_DATA_TRANSMITTED = 0x01
+
+
+class AssistedListeningStream(utils.OpenIntEnum):
+    UNSPECIFIED_AUDIO_ENHANCEMENT = 0x00
+
+
@dataclasses.dataclass
 class Metadata:
    '''Bluetooth Assigned Numbers, Section 6.12.6 - Metadata LTV structures.

-    As Metadata fields may extend, and Spec doesn't forbid duplication, we don't parse
-    Metadata into a key-value style dataclass here. Rather, we encourage users to parse
-    again outside the lib.
+    As Metadata fields may extend, and the spec may not guarantee the uniqueness of
+    tags, we don't automatically parse the Metadata data into specific classes.
+    Users of this class may decode the data by themselves, or use the Entry.decode
+    method.
    '''

    class Tag(utils.OpenIntEnum):
@@ -57,6 +69,44 @@ class Metadata:
        tag: Metadata.Tag
        data: bytes

+        def decode(self) -> Any:
+            """
+            Decode the data into an object, if possible.
+
+            If no specific object class exists to represent the data, the raw data
+            bytes are returned.
+            """
+
+            if self.tag in (
+                Metadata.Tag.PREFERRED_AUDIO_CONTEXTS,
+                Metadata.Tag.STREAMING_AUDIO_CONTEXTS,
+            ):
+                return bap.ContextType(struct.unpack("<H", self.data)[0])
+
+            if self.tag in (
+                Metadata.Tag.PROGRAM_INFO,
+                Metadata.Tag.PROGRAM_INFO_URI,
+                Metadata.Tag.BROADCAST_NAME,
+            ):
+                return self.data.decode("utf-8")
+
+            if self.tag == Metadata.Tag.LANGUAGE:
+                return self.data.decode("ascii")
+
+            if self.tag == Metadata.Tag.CCID_LIST:
+                return list(self.data)
+
+            if self.tag == Metadata.Tag.PARENTAL_RATING:
+                return self.data[0]
+
+            if self.tag == Metadata.Tag.AUDIO_ACTIVE_STATE:
+                return AudioActiveState(self.data[0])
+
+            if self.tag == Metadata.Tag.ASSISTED_LISTENING_STREAM:
+                return AssistedListeningStream(self.data[0])
+
+            return self.data
+
        @classmethod
        def from_bytes(cls: Type[Self], data: bytes) -> Self:
            return cls(tag=Metadata.Tag(data[0]), data=data[1:])
@@ -66,6 +116,29 @@ class Metadata:

    entries: List[Entry] = dataclasses.field(default_factory=list)

+    def pretty_print(self, indent: str) -> str:
+        """Convenience method to generate a string with one key-value pair per line."""
+
+        max_key_length = 0
+        keys = []
+        values = []
+        for entry in self.entries:
+            key = entry.tag.name
+            max_key_length = max(max_key_length, len(key))
+            keys.append(key)
+            decoded = entry.decode()
+            if isinstance(decoded, enum.Enum):
+                values.append(decoded.name)
+            elif isinstance(decoded, bytes):
+                values.append(decoded.hex())
+            else:
+                values.append(str(decoded))
+
+        return '\n'.join(
+            f'{indent}{key}: {" " * (max_key_length-len(key))}{value}'
+            for key, value in zip(keys, values)
+        )
+
    @classmethod
    def from_bytes(cls: Type[Self], data: bytes) -> Self:
        entries = []
@@ -81,3 +154,13 @@ class Metadata:

    def __bytes__(self) -> bytes:
        return b''.join([bytes(entry) for entry in self.entries])
+
+    def __str__(self) -> str:
+        entries_str = []
+        for entry in self.entries:
+            decoded = entry.decode()
+            entries_str.append(
+                f'{entry.tag.name}: '
+                f'{decoded.hex() if isinstance(decoded, bytes) else decoded!r}'
+            )
+        return f'Metadata(entries={", ".join(entry_str for entry_str in entries_str)})'
--- a/bumble/profiles/pacs.py
+++ b/bumble/profiles/pacs.py
@@ -72,6 +72,19 @@ class PacRecord:
            metadata=metadata,
        )

+    @classmethod
+    def list_from_bytes(cls, data: bytes) -> list[PacRecord]:
+        """Parse a serialized list of records preceded by a one byte list length."""
+        record_count = data[0]
+        records = []
+        offset = 1
+        for _ in range(record_count):
+            record = PacRecord.from_bytes(data[offset:])
+            offset += len(bytes(record))
+            records.append(record)
+
+        return records
+
    def __bytes__(self) -> bytes:
        capabilities_bytes = bytes(self.codec_specific_capabilities)
        metadata_bytes = bytes(self.metadata)
@@ -172,39 +185,58 @@ class PublishedAudioCapabilitiesService(gatt.TemplateService):
 class PublishedAudioCapabilitiesServiceProxy(gatt_client.ProfileServiceProxy):
    SERVICE_CLASS = PublishedAudioCapabilitiesService

-    sink_pac: Optional[gatt_client.CharacteristicProxy] = None
-    sink_audio_locations: Optional[gatt_client.CharacteristicProxy] = None
-    source_pac: Optional[gatt_client.CharacteristicProxy] = None
-    source_audio_locations: Optional[gatt_client.CharacteristicProxy] = None
-    available_audio_contexts: gatt_client.CharacteristicProxy
-    supported_audio_contexts: gatt_client.CharacteristicProxy
+    sink_pac: Optional[gatt.DelegatedCharacteristicAdapter] = None
+    sink_audio_locations: Optional[gatt.DelegatedCharacteristicAdapter] = None
+    source_pac: Optional[gatt.DelegatedCharacteristicAdapter] = None
+    source_audio_locations: Optional[gatt.DelegatedCharacteristicAdapter] = None
+    available_audio_contexts: gatt.DelegatedCharacteristicAdapter
+    supported_audio_contexts: gatt.DelegatedCharacteristicAdapter

    def __init__(self, service_proxy: gatt_client.ServiceProxy):
        self.service_proxy = service_proxy

-        self.available_audio_contexts = service_proxy.get_characteristics_by_uuid(
-            gatt.GATT_AVAILABLE_AUDIO_CONTEXTS_CHARACTERISTIC
-        )[0]
-        self.supported_audio_contexts = service_proxy.get_characteristics_by_uuid(
-            gatt.GATT_SUPPORTED_AUDIO_CONTEXTS_CHARACTERISTIC
-        )[0]
+        self.available_audio_contexts = gatt.DelegatedCharacteristicAdapter(
+            service_proxy.get_required_characteristic_by_uuid(
+                gatt.GATT_AVAILABLE_AUDIO_CONTEXTS_CHARACTERISTIC
+            ),
+            decode=lambda x: tuple(map(ContextType, struct.unpack('<HH', x))),
+        )
+
+        self.supported_audio_contexts = gatt.DelegatedCharacteristicAdapter(
+            service_proxy.get_required_characteristic_by_uuid(
+                gatt.GATT_SUPPORTED_AUDIO_CONTEXTS_CHARACTERISTIC
+            ),
+            decode=lambda x: tuple(map(ContextType, struct.unpack('<HH', x))),
+        )

        if characteristics := service_proxy.get_characteristics_by_uuid(
            gatt.GATT_SINK_PAC_CHARACTERISTIC
        ):
-            self.sink_pac = characteristics[0]
+            self.sink_pac = gatt.DelegatedCharacteristicAdapter(
+                characteristics[0],
+                decode=PacRecord.list_from_bytes,
+            )

        if characteristics := service_proxy.get_characteristics_by_uuid(
            gatt.GATT_SOURCE_PAC_CHARACTERISTIC
        ):
-            self.source_pac = characteristics[0]
+            self.source_pac = gatt.DelegatedCharacteristicAdapter(
+                characteristics[0],
+                decode=PacRecord.list_from_bytes,
+            )

        if characteristics := service_proxy.get_characteristics_by_uuid(
            gatt.GATT_SINK_AUDIO_LOCATION_CHARACTERISTIC
        ):
-            self.sink_audio_locations = characteristics[0]
+            self.sink_audio_locations = gatt.DelegatedCharacteristicAdapter(
+                characteristics[0],
+                decode=lambda x: AudioLocation(struct.unpack('<I', x)[0]),
+            )

        if characteristics := service_proxy.get_characteristics_by_uuid(
            gatt.GATT_SOURCE_AUDIO_LOCATION_CHARACTERISTIC
        ):
-            self.source_audio_locations = characteristics[0]
+            self.source_audio_locations = gatt.DelegatedCharacteristicAdapter(
+                characteristics[0],
+                decode=lambda x: AudioLocation(struct.unpack('<I', x)[0]),
+            )
--- a/bumble/profiles/tmap.py
+++ b/bumble/profiles/tmap.py
@@ -25,7 +25,6 @@ from bumble.gatt import (
    TemplateService,
    Characteristic,
    DelegatedCharacteristicAdapter,
-    InvalidServiceError,
    GATT_TELEPHONY_AND_MEDIA_AUDIO_SERVICE,
    GATT_TMAP_ROLE_CHARACTERISTIC,
 )
@@ -74,15 +73,10 @@ class TelephonyAndMediaAudioServiceProxy(ProfileServiceProxy):
    def __init__(self, service_proxy: ServiceProxy):
        self.service_proxy = service_proxy

-        if not (
-            characteristics := service_proxy.get_characteristics_by_uuid(
-                GATT_TMAP_ROLE_CHARACTERISTIC
-            )
-        ):
-            raise InvalidServiceError('TMAP Role characteristic not found')
-
        self.role = DelegatedCharacteristicAdapter(
-            characteristics[0],
+            service_proxy.get_required_characteristic_by_uuid(
+                GATT_TMAP_ROLE_CHARACTERISTIC
+            ),
            decode=lambda value: Role(
                struct.unpack_from('<H', value, 0)[0],
            ),
--- a/bumble/profiles/vcs.py
+++ b/bumble/profiles/vcs.py
@@ -1,4 +1,4 @@
-# Copyright 2021-2024 Google LLC
+# Copyright 2021-2025 Google LLC
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -17,14 +17,16 @@
 # Imports
 # -----------------------------------------------------------------------------
 from __future__ import annotations
+import dataclasses
 import enum

+from typing import Optional, Sequence
+
 from bumble import att
 from bumble import device
 from bumble import gatt
 from bumble import gatt_client

-from typing import Optional, Sequence

 # -----------------------------------------------------------------------------
 # Constants
@@ -67,6 +69,20 @@ class VolumeControlPointOpcode(enum.IntEnum):
    MUTE                        = 0x06


+@dataclasses.dataclass
+class VolumeState:
+    volume_setting: int
+    mute: int
+    change_counter: int
+
+    @classmethod
+    def from_bytes(cls, data: bytes) -> VolumeState:
+        return cls(data[0], data[1], data[2])
+
+    def __bytes__(self) -> bytes:
+        return bytes([self.volume_setting, self.mute, self.change_counter])
+
+
 # -----------------------------------------------------------------------------
 # Server
 # -----------------------------------------------------------------------------
@@ -126,16 +142,8 @@ class VolumeControlService(gatt.TemplateService):
            included_services=list(included_services),
        )

-    @property
-    def volume_state_bytes(self) -> bytes:
-        return bytes([self.volume_setting, self.muted, self.change_counter])
-
-    @volume_state_bytes.setter
-    def volume_state_bytes(self, new_value: bytes) -> None:
-        self.volume_setting, self.muted, self.change_counter = new_value
-
    def _on_read_volume_state(self, _connection: Optional[device.Connection]) -> bytes:
-        return self.volume_state_bytes
+        return bytes(VolumeState(self.volume_setting, self.muted, self.change_counter))

    def _on_write_volume_control_point(
        self, connection: Optional[device.Connection], value: bytes
@@ -153,14 +161,9 @@ class VolumeControlService(gatt.TemplateService):
            self.change_counter = (self.change_counter + 1) % 256
            connection.abort_on(
                'disconnection',
-                connection.device.notify_subscribers(
-                    attribute=self.volume_state,
-                    value=self.volume_state_bytes,
-                ),
-            )
-            self.emit(
-                'volume_state', self.volume_setting, self.muted, self.change_counter
+                connection.device.notify_subscribers(attribute=self.volume_state),
            )
+            self.emit('volume_state_change')

    def _on_relative_volume_down(self) -> bool:
        old_volume = self.volume_setting
@@ -207,24 +210,26 @@ class VolumeControlServiceProxy(gatt_client.ProfileServiceProxy):
    SERVICE_CLASS = VolumeControlService

    volume_control_point: gatt_client.CharacteristicProxy
+    volume_state: gatt.SerializableCharacteristicAdapter
+    volume_flags: gatt.DelegatedCharacteristicAdapter

    def __init__(self, service_proxy: gatt_client.ServiceProxy) -> None:
        self.service_proxy = service_proxy

-        self.volume_state = gatt.PackedCharacteristicAdapter(
-            service_proxy.get_characteristics_by_uuid(
+        self.volume_state = gatt.SerializableCharacteristicAdapter(
+            service_proxy.get_required_characteristic_by_uuid(
                gatt.GATT_VOLUME_STATE_CHARACTERISTIC
-            )[0],
-            'BBB',
+            ),
+            VolumeState,
        )

-        self.volume_control_point = service_proxy.get_characteristics_by_uuid(
+        self.volume_control_point = service_proxy.get_required_characteristic_by_uuid(
            gatt.GATT_VOLUME_CONTROL_POINT_CHARACTERISTIC
-        )[0]
-
-        self.volume_flags = gatt.PackedCharacteristicAdapter(
-            service_proxy.get_characteristics_by_uuid(
-                gatt.GATT_VOLUME_FLAGS_CHARACTERISTIC
-            )[0],
-            'B',
+        )
+
+        self.volume_flags = gatt.DelegatedCharacteristicAdapter(
+            service_proxy.get_required_characteristic_by_uuid(
+                gatt.GATT_VOLUME_FLAGS_CHARACTERISTIC
+            ),
+            decode=lambda data: VolumeFlags(data[0]),
        )
--- a/bumble/profiles/vocs.py
+++ b/bumble/profiles/vocs.py
@@ -27,8 +27,8 @@ from bumble.gatt import (
    DelegatedCharacteristicAdapter,
    TemplateService,
    CharacteristicValue,
+    SerializableCharacteristicAdapter,
    UTF8CharacteristicAdapter,
-    InvalidServiceError,
    GATT_VOLUME_OFFSET_CONTROL_SERVICE,
    GATT_VOLUME_OFFSET_STATE_CHARACTERISTIC,
    GATT_AUDIO_LOCATION_CHARACTERISTIC,
@@ -82,9 +82,7 @@ class VolumeOffsetState:

    async def notify_subscribers_via_connection(self, connection: Connection) -> None:
        assert self.attribute_value is not None
-        await connection.device.notify_subscribers(
-            attribute=self.attribute_value, value=bytes(self)
-        )
+        await connection.device.notify_subscribers(attribute=self.attribute_value)

    def on_read(self, _connection: Optional[Connection]) -> bytes:
        return bytes(self)
@@ -111,9 +109,7 @@ class VocsAudioLocation:
        assert self.attribute_value

        self.audio_location = AudioLocation(int.from_bytes(value, 'little'))
-        await connection.device.notify_subscribers(
-            attribute=self.attribute_value, value=value
-        )
+        await connection.device.notify_subscribers(attribute=self.attribute_value)


@dataclass
@@ -169,9 +165,7 @@ class AudioOutputDescription:
        assert self.attribute_value

        self.audio_output_description = value.decode('utf-8')
-        await connection.device.notify_subscribers(
-            attribute=self.attribute_value, value=value
-        )
+        await connection.device.notify_subscribers(attribute=self.attribute_value)


 # -----------------------------------------------------------------------------
@@ -203,37 +197,30 @@ class VolumeOffsetControlService(TemplateService):
            VolumeOffsetControlPoint(self.volume_offset_state)
        )

-        self.volume_offset_state_characteristic = DelegatedCharacteristicAdapter(
-            Characteristic(
-                uuid=GATT_VOLUME_OFFSET_STATE_CHARACTERISTIC,
-                properties=(
-                    Characteristic.Properties.READ | Characteristic.Properties.NOTIFY
-                ),
-                permissions=Characteristic.Permissions.READ_REQUIRES_ENCRYPTION,
-                value=CharacteristicValue(read=self.volume_offset_state.on_read),
+        self.volume_offset_state_characteristic = Characteristic(
+            uuid=GATT_VOLUME_OFFSET_STATE_CHARACTERISTIC,
+            properties=(
+                Characteristic.Properties.READ | Characteristic.Properties.NOTIFY
            ),
-            encode=lambda value: bytes(value),
+            permissions=Characteristic.Permissions.READ_REQUIRES_ENCRYPTION,
+            value=CharacteristicValue(read=self.volume_offset_state.on_read),
        )

-        self.audio_location_characteristic = DelegatedCharacteristicAdapter(
-            Characteristic(
-                uuid=GATT_AUDIO_LOCATION_CHARACTERISTIC,
-                properties=(
-                    Characteristic.Properties.READ
-                    | Characteristic.Properties.NOTIFY
-                    | Characteristic.Properties.WRITE_WITHOUT_RESPONSE
-                ),
-                permissions=(
-                    Characteristic.Permissions.READ_REQUIRES_ENCRYPTION
-                    | Characteristic.Permissions.WRITE_REQUIRES_ENCRYPTION
-                ),
-                value=CharacteristicValue(
-                    read=self.audio_location.on_read,
-                    write=self.audio_location.on_write,
-                ),
+        self.audio_location_characteristic = Characteristic(
+            uuid=GATT_AUDIO_LOCATION_CHARACTERISTIC,
+            properties=(
+                Characteristic.Properties.READ
+                | Characteristic.Properties.NOTIFY
+                | Characteristic.Properties.WRITE_WITHOUT_RESPONSE
+            ),
+            permissions=(
+                Characteristic.Permissions.READ_REQUIRES_ENCRYPTION
+                | Characteristic.Permissions.WRITE_REQUIRES_ENCRYPTION
+            ),
+            value=CharacteristicValue(
+                read=self.audio_location.on_read,
+                write=self.audio_location.on_write,
            ),
-            encode=lambda value: bytes(value),
-            decode=VocsAudioLocation.from_bytes,
        )
        self.audio_location.attribute_value = self.audio_location_characteristic.value

@@ -244,25 +231,22 @@ class VolumeOffsetControlService(TemplateService):
            value=CharacteristicValue(write=self.volume_offset_control_point.on_write),
        )

-        self.audio_output_description_characteristic = DelegatedCharacteristicAdapter(
-            Characteristic(
-                uuid=GATT_AUDIO_OUTPUT_DESCRIPTION_CHARACTERISTIC,
-                properties=(
-                    Characteristic.Properties.READ
-                    | Characteristic.Properties.NOTIFY
-                    | Characteristic.Properties.WRITE_WITHOUT_RESPONSE
-                ),
-                permissions=(
-                    Characteristic.Permissions.READ_REQUIRES_ENCRYPTION
-                    | Characteristic.Permissions.WRITE_REQUIRES_ENCRYPTION
-                ),
-                value=CharacteristicValue(
-                    read=self.audio_output_description.on_read,
-                    write=self.audio_output_description.on_write,
-                ),
-            )
+        self.audio_output_description_characteristic = Characteristic(
+            uuid=GATT_AUDIO_OUTPUT_DESCRIPTION_CHARACTERISTIC,
+            properties=(
+                Characteristic.Properties.READ
+                | Characteristic.Properties.NOTIFY
+                | Characteristic.Properties.WRITE_WITHOUT_RESPONSE
+            ),
+            permissions=(
+                Characteristic.Permissions.READ_REQUIRES_ENCRYPTION
+                | Characteristic.Permissions.WRITE_REQUIRES_ENCRYPTION
+            ),
+            value=CharacteristicValue(
+                read=self.audio_output_description.on_read,
+                write=self.audio_output_description.on_write,
+            ),
        )
-
        self.audio_output_description.attribute_value = (
            self.audio_output_description_characteristic.value
        )
@@ -287,44 +271,29 @@ class VolumeOffsetControlServiceProxy(ProfileServiceProxy):
    def __init__(self, service_proxy: ServiceProxy) -> None:
        self.service_proxy = service_proxy

-        if not (
-            characteristics := service_proxy.get_characteristics_by_uuid(
+        self.volume_offset_state = SerializableCharacteristicAdapter(
+            service_proxy.get_required_characteristic_by_uuid(
                GATT_VOLUME_OFFSET_STATE_CHARACTERISTIC
-            )
-        ):
-            raise InvalidServiceError("Volume Offset State characteristic not found")
-        self.volume_offset_state = DelegatedCharacteristicAdapter(
-            characteristics[0], decode=VolumeOffsetState.from_bytes
+            ),
+            VolumeOffsetState,
        )

-        if not (
-            characteristics := service_proxy.get_characteristics_by_uuid(
-                GATT_AUDIO_LOCATION_CHARACTERISTIC
-            )
-        ):
-            raise InvalidServiceError("Audio Location characteristic not found")
        self.audio_location = DelegatedCharacteristicAdapter(
-            characteristics[0],
-            encode=lambda value: bytes(value),
-            decode=VocsAudioLocation.from_bytes,
+            service_proxy.get_required_characteristic_by_uuid(
+                GATT_AUDIO_LOCATION_CHARACTERISTIC
+            ),
+            encode=lambda value: bytes([int(value)]),
+            decode=lambda data: AudioLocation(data[0]),
        )

-        if not (
-            characteristics := service_proxy.get_characteristics_by_uuid(
+        self.volume_offset_control_point = (
+            service_proxy.get_required_characteristic_by_uuid(
                GATT_VOLUME_OFFSET_CONTROL_POINT_CHARACTERISTIC
            )
-        ):
-            raise InvalidServiceError(
-                "Volume Offset Control Point characteristic not found"
-            )
-        self.volume_offset_control_point = characteristics[0]
+        )

-        if not (
-            characteristics := service_proxy.get_characteristics_by_uuid(
+        self.audio_output_description = UTF8CharacteristicAdapter(
+            service_proxy.get_required_characteristic_by_uuid(
                GATT_AUDIO_OUTPUT_DESCRIPTION_CHARACTERISTIC
            )
-        ):
-            raise InvalidServiceError(
-                "Audio Output Description characteristic not found"
-            )
-        self.audio_output_description = UTF8CharacteristicAdapter(characteristics[0])
+        )