ChromeOS Compatible - Speakermic Specification v1.3

Version: 1.3
Last updated: 2024-09-06

Legend

Product Verb	Development Action
"MUST"	Mandatory product requirement
"SHOULD"	Optional recommendation
"MAY"	Nice to have

Overview

This document describes the requirements a ChromeOS Compatible USB+Bluetooth speaker-mic meets. This specification is not for WWCB products, nor for a product designed and certified together with a Chromebook.

USB

Security

2.4 GHz Wireless Dongle

The 2.4 GHz wireless device only auto-pairs with the receiver (dongle) that comes with the box.
User action (either on the device or via an app) is required to pair headset with another receiver or pair new headset with existing receiver.
If an app is required to alter headset/receiver pairing, the app must run on ChromeOS, such as via an extension. The app can also be a web app using WebUSB/WebHID.
If the pairing is implemented via an extension, the extension must only have access to USB ports. Content scripts are explicitly disallowed.

Firmware and Connector

Headset must be declared as an audio device with a correct audio interface (0x01) descriptor.
- There must be one corresponding descriptor for both input and output terminal.
  - It is recommended to report the USB Audio Class (UAC) terminal type
    - Headset (0x0402)
    - SpeakerPhone (0x0403-0x0405) .
If it has any button, it has to be declared as an HID.
The headset must meet the WWCB Firmware and Connector requirements.

Software

Format

Please refer to Audio Format.

For device have both input and output Audio Interface Descriptor.

Example of Audio Interface Descriptor

Interface Descriptor:
  bLength                 9
  bDescriptorType         4
  bInterfaceNumber        2
  bAlternateSetting       0
  bNumEndpoints           0
  bInterfaceClass         1 Audio
  bInterfaceSubClass      2 Streaming
  bInterfaceProtocol      0
  iInterface              0

If the sample rates of the input and output are different, the device must be able to support playback and capture at different sample rates at the same time. Otherwise, the device must reflect the same value in the AudioStreaming Interface Descriptor -> tSamFreq.

Example of 48k USB audio output sample rate

AudioStreaming Interface Descriptor:
  bLength                11
  bDescriptorType        36
  bDescriptorSubtype      2 (FORMAT_TYPE)
  bFormatType             1 (FORMAT_TYPE_I)
  bNrChannels             2
  bSubframeSize           2
  bBitResolution         16
  bSamFreqType            1 Discrete
  tSamFreq[ 0]        48000
Endpoint Descriptor:
  bLength                 9
  bDescriptorType         5
  bEndpointAddress     0x02  EP 2 OUT(Output)
  bmAttributes            9
    Transfer Type            Isochronous
    Synch Type               Adaptive
    Usage Type               Data

Example of 44.1k USB audio input sample rate

AudioStreaming Interface Descriptor:
  bLength                11
  bDescriptorType        36
  bDescriptorSubtype      2 (FORMAT_TYPE)
  bFormatType             1 (FORMAT_TYPE_I)
  bNrChannels             2
  bSubframeSize           2
  bBitResolution         16
  bSamFreqType            1 Discrete
  tSamFreq[ 0]        44100
Endpoint Descriptor:
  bLength                 9
  bDescriptorType         5
  bEndpointAddress     0x81  EP 1 In(Input)
  bmAttributes            9
    Transfer Type            Isochronous
    Synch Type               Adaptive
    Usage Type               Data

HID Codes

For each HID event, it can only transmit one event once a time.
The correct event code and corresponding event code should be received when the button is pressed.
- For example, increase the volume. evtest can only observe one volume up event and the code must be KEY_VOLUME_UP.
If there is any interface designed to provide following functionalities, the USB peripheral must support emitting or receiving the corresponding HID events according to USB.org HID specification.

Consumer Page (0x0c)

Key Name	HID usage ID	Usage Type
`KEY_PLAY`	`0x0b0`	OOC
`KEY_PAUSE`	`0x0b1`	OOC
`KEY_NEXTSONG`	`0x0b5`	OSC
`KEY_PREVIOUSSONG`	`0x0b6`	OSC
`KEY_STOPCD`	`0x0b7`	OSC
`KEY_PLAYPAUSE`	`0x0cd`	OSC
`KEY_PREVIOUSSONG`	`0x0b6`	OSC
`KEY_MUTE`	`0x0e2`	OOC
`KEY_VOLUMEUP`	`0x0e9`	RTC
`KEY_VOLUMEDOWN`	`0x0ea`	RTC

Telephony Page (0x0b)

Key Name	HID usage ID	Usage Type
Hook Switch	`0x20`	OOC
Ringer	`0x9e`	OOC

LED Page (0x08)

Key Name	HID usage ID	Usage Type
Mute	`0x09`	OOC
Off-Hook	`0x17`	OOC
Ring	`0x18`	OOC

Jack Detection

If a USB device does not support USB Audio Class (UAC), it will always show an output node in the ChromeOS system tray. However, if the USB device supports UAC, the system will be able to correctly detect a 3.5mm audio jack when the device is inserted.

CrOS Must use presence detection for 3.5mm jacks
- Must perform insert detect via one of:
  - UAC1
  - UAC2
  - UAC3

General Bluetooth Requirements

Refer to ChromeOS Compatible - Bluetooth Specification.

Audio Format

	Playback	Recording
Sample rate	≥ 16 kHz	≥ 16 kHz
Format	S16_LE	S16_LE

The channel number and configuration must be correct.
All sampling rates the headset declares supported must work correctly.
- The deviation between measured rate and sampling rate must be ≤ 0.1% .
- The standard error for linear regression of measured rate must be < 30.
The headset must support playback or capture under different sample rates it asserts to support.

For example, play audio under 44.1 kHz but capture voice under 48 kHz simultaneously.
- Otherwise, it requires ChromeOS to add a specific configuration file to prevent it on the system side.

Audio Quality

Capture Path - Mute

If there is any interface for users to mute the audio device, it must
- Maintain the mute state in a way that is not affected by:
  - Opening and closing the device.
  - Switching to another input device.
If the user presses the mute button on the headset or ChromeOS, the mute state must change.
If the mute state changes, the mute state indicator (eg:LED) on the headset must change.

Audio Latency

Latency

Output Latency
- Audio playback must begin ≤500 ms after a user action that initiates playback.
  - May request a waiver if the device OEM can prove that no echo is introduced when it fails this requirement.

A/V Sync

Audio playback should be synchronized with video playback. Audio playback may lead the video by ≤25 ms or trail the video by ≤95 ms.

Revision History

Date	Version	Notes
2024-09-06	1.3	ChromeOS Compatible spec derived. Initial Partner Site Publication.
2022-09-14	1.2	Updated to v1.2.
2022-08-19	1.1	Updated to v1.1.
2022-08-18	1.0	Related WWCB specification created.