"cenc" Initialization Data Format

Abstract

This specification defines the "cenc" initialization data format for use with the Encrypted Media Extensions [ENCRYPTED-MEDIA]. This format is commonly used with the ISO Common Encryption ('cenc') Protection Scheme for ISO Base Media File Format Stream Format [EME-STREAM-REGISTRY].

This specification also defines a common SystemID and PSSH box format for use with Encrypted Media Extensions.

Note

This format's initialization data type string "cenc" refers to the [CENC] spec that defines the PSSH boxes that comprise the format. It does not relate to or imply a stream format, including the use of the 'cenc' protection scheme. Stream formats are indicated by the content types as defined in the Encrypted Media Extensions Stream Format Registry [EME-STREAM-REGISTRY].

Status of This Document

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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.

The format is one or more concatenated Protection System Specific Header ('pssh') boxes [CENC], each for a unique SystemID. One of the concatenated 'pssh' boxes SHOULD use the Common SystemID and PSSH Box Format.

Note

[CENC] also specifies storage of a 'pssh' box base64-encoded in an XML element of the form <cenc:pssh (base64 'pssh')>. For example, [MPEGDASH] manifests may provide 'pssh' boxes in this format, each contained in a ContentProtection Descriptor element identified by a SystemID. These 'pssh' boxes may be decoded and concatenated by an application to provide equivalent Initialization Data to that stored in movie or movie fragment boxes.

This section defines a common open SystemID and PSSH box format. Key System implementations supporting the "cenc" Initialization Data Format MUST support this SystemID and format. Media resources for use with Encrypted Media Extensions SHOULD contain appropriate PSSH box(es) for this SystemID.

Note

Use of this SystemID is RECOMMENDED for applications, packagers, and implementors. Use of other SystemIDs with the Encrypted Media Extensions APIs is discouraged. 'pssh' box(es) for this SystemID SHOULD be included in all new or repackaged content so that the content can be used with any compliant Key System. For existing content, applications may alternatively obtain a 'pssh' box containing this SystemID or another Initialization Data Type (e.g., "keyids" Initialization Data Format [EME-STREAM-REGISTRY]) from another source.

Note

Implementations MAY support other SystemIDs for backwards compatibility with existing streams.

The SystemID is 1077efec-c0b2-4d02-ace3-3c1e52e2fb4b.

The PSSH box format is as follows. It follows version 1 of the 'pssh' box as defined in [CENC].

version: 1
KID and KID_count: The key ID(s) represented by the PSSH box. For example, those key ID(s) used by the Movie ('moov') or Movie Fragment ('moof').
Data and DataSize: Reserved for future use. DataSize SHALL be set to 0 when constructing this box. When processing, if dataSize is non-zero the Data field SHALL be ignored.

This section is non-normative.

The following example contains two key IDs.

Example 1

var pssh = [
    0x00, 0x00, 0x00, 0x44, 0x70, 0x73, 0x73, 0x68, // BMFF box header (68 bytes, 'pssh')
    0x01, 0x00, 0x00, 0x00,                         // Full box header (version = 1, flags = 0)
    0x10, 0x77, 0xef, 0xec, 0xc0, 0xb2, 0x4d, 0x02, // SystemID
    0xac, 0xe3, 0x3c, 0x1e, 0x52, 0xe2, 0xfb, 0x4b,
    0x00, 0x00, 0x00, 0x02,                         // KID_count (2)
    0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, // First KID ("0123456789012345")
    0x38, 0x39, 0x30, 0x31, 0x32, 0x33, 0x34, 0x35,
    0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, // Second KID ("ABCDEFGHIJKLMNOP")
    0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f, 0x50,
    0x00, 0x00, 0x00, 0x00,                         // Size of Data (0)
];

"cenc" Initialization Data Format

Abstract

Status of This Document

1. Format

2. Processing

3. Use with Clear Key

4. Common SystemID and PSSH Box Format

4.1 Definition

4.2 Example

5. Conformance

A. References

A.1 Normative references

A.2 Informative references