WebM Stream Format

Status of This Document

This section describes the status of this document at the time of its publication. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at https://www.w3.org/TR/.

This document was published by the Media Working Group as an Editor's Draft.

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This document is governed by the 03 November 2023 W3C Process Document.

Encrypted WebM streams [WebM-Encryption] are encrypted at the block level with AES-128 CTR encryption. The container SHALL include appropriate values within the ContentEncryption [Matroska] element.

WebM streams may be partially encrypted, both at the Track level and the block level. In the former case, a subset of Tracks in the stream have a ContentEncryption element. In the latter case, a subset of the blocks within a Track containing a ContentEncryption element are marked as encrypted.

Initialization Data is always a single key ID, as defined by the "webm" Initialization Data Format [EME-INITDATA-REGISTRY].

Each time a ContentEncKeyID [Matroska] element is encountered in a Track, the Initialization Data Encountered algorithm SHALL be invoked with initDataType = "webm" [EME-INITDATA-REGISTRY] and initData = the value in that element.

As well as sections marked as non-normative, all authoring guidelines, diagrams, examples, and notes in this specification are non-normative. Everything else in this specification is normative.

The key word SHALL in this document is to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

[EME-INITDATA-REGISTRY]: Encrypted Media Extensions Initialization Data Format Registry. David Dorwin; Adrian Bateman; Mark Watson. W3C. 15 September 2016. W3C Working Group Note. URL: https://www.w3.org/TR/eme-initdata-registry/
[EME-INITDATA-WEBM]: "webm" Initialization Data Format. Joey Parrish; Greg Freedman. W3C. 18 July 2024. W3C Working Group Note. URL: https://www.w3.org/TR/eme-initdata-webm/
[ENCRYPTED-MEDIA]: Encrypted Media Extensions. David Dorwin; Jerry Smith; Mark Watson; Adrian Bateman. W3C. 18 September 2017. W3C Recommendation. URL: https://www.w3.org/TR/encrypted-media-1/
[Matroska]: Matroska Specifications. Matroska. 9 January 2014. URL: https://matroska.org/technical/specs/index.html
[RFC2119]: Key words for use in RFCs to Indicate Requirement Levels. S. Bradner. IETF. March 1997. Best Current Practice. URL: https://www.rfc-editor.org/rfc/rfc2119
[RFC8174]: Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words. B. Leiba. IETF. May 2017. Best Current Practice. URL: https://www.rfc-editor.org/rfc/rfc8174
[WebM]: WebM Container Guidelines. The WebM Project. 26 April 2016. URL: https://www.webmproject.org/docs/container/
[WebM-Encryption]: WebM Encryption. Frank Galligan. The WebM Project. 4 March 2015. URL: https://www.webmproject.org/docs/webm-encryption/

WebM Stream Format

Abstract

Status of This Document

1. Stream Format

2. Detection

3. Detecting Encrypted Blocks

4. Initialization Data Extraction

5. Conformance

A. References

A.1 Normative references