A/338, “Companion Device”Approved: 14 April 2026

This document specifies the communication protocol between an ATSC 3.0 primary device and an ATSC 3.0 companion device. In this context, the primary device is the primary receiver and is used to present the primary content. The companion device communicates with the primary device to present related, supplementary content, or even the same content as that being presented on the primary device. Examples of primary devices include television sets, set-top/converter boxes, and mobile devices that are capable of receiving ATSC 3.0 services. Examples of companion devices are laptops, tablets, and smartphones.

Download current version: A/338:2026-04, “Companion Device”, 14 April 2026. Schema files can be found here: atsc-schemas.org. This version of the Standard is normatively referenced in A/300:2026-04.

Previous Versions

There are multiple versions of this document. Please be sure to download the desired version. For amendments, the text includes a list of changes, the rationale for the changes, and compatibility considerations. The following documents are listed by date, with the most recent first.

2025

Download A/338:2025-07, “Companion Device”, 17 July 2025. This version of the Standard is normatively referenced in A/300:2025-07.

2024

Download A/338:2024-04, “Companion Device”, 3 April 2024, and accompanying schema. This version of the Standard is normatively referenced in A/300:2024-04.

2023

Download A/338:2023-03, “Companion Device”, and accompanying schema, 28 March 2023. This version of the Standard is normatively referenced in A/300:2023-03.

2022

Download A/338:2022-03, “Companion Device”, and accompanying schema, 31 March 2022. This version of the Standard is normatively referenced in A/300:2022-04.

Download A/338:2022-01, “Companion Device”, approved 17 January 2022, and accompanying schema.

2021

Download A/338:2021, “Companion Device”, approved 19 February 2021. This version of the Standard is normatively referenced in A/300:2021.

2019

Download A/338:2019 “Companion Device”, approved 2 October 2019. This version of the Standard is normatively referenced in A/300:2020.

Download A/338:2019 Amendment No. 1, “CD Event Stream API”, approved 21 January 2020.

2017

Download A/338:2017, “Companion Device”, approved 17 April 2017. This version of the Standard is normatively referenced in A/300:2019.