faushine1 3e854f4c90 feat: add subsample encryption support for Dolby AC-4 (#1522) ...

**Description**

This PR introduces support for subsample encryption for Dolby AC-4 audio
streams including muxing and packaging in Shaka Pakager.

**Motivation**

Subsample encryption is a mode of Common Encryption (CENC) that allows
selective encryption of media samples, leaving specific portions (such
as headers) in the clear. In most cases, subsample encryption is applied
to video streams (e.g., H.265/HEVC or AV1). It can also be used for
audio streams, even though many pipelines default to full-sample
encryption for audio. For Dolby AC-4, this is particularly useful
because the AC-4 frame header (ac4_toc) contains configuration data that
must remain accessible to parsers and playback systems even when the
rest of the frame is encrypted.
By implementing subsample encryption for AC-4:
- Parsers can validate and process encrypted streams without full
decryption.
- Playback systems can perform certain bitstream operations (e.g.,
stream identification, sync validation) efficiently.
- This aligns with best practices for encrypted media delivery and
improves performance with streaming platforms.

**Implementation Details**

- The implementation ensures that the ac4_toc() portion of each AC-4
frame remains unencrypted.
- The remaining payload is encrypted using the selected CENC protection
scheme (e.g., cbcs or cenc).

**Specification Reference**

This feature is not mentioned in any published specification. However,
it is discussed in detail in the specification, which has not yet been
publicly released but is expected to be published in the near future.
Once available, it will provide formal guidance on subsample encryption
for AC-4, including the handling of the ac4_toc() structure and
encryption boundaries.

**Notes**

- This implementation is compatible with the upcoming public release of
the AC-4 ISOBMFF specification.
- The feature has been tested on encryption/decryption, DASH, HLS, and
DRM. The generated content is conforms to expected encryption behavior.
- Additional documentation will be provided once the specification is
officially published.

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Co-authored-by: Xingzhao Yun <xyun@dolby.com>

2026-03-09 09:06:58 -07:00

..

output

feat: add subsample encryption support for Dolby AC-4 (#1522)

2026-03-09 09:06:58 -07:00

stream.mpd

feat: add subsample encryption support for Dolby AC-4 (#1522)

2026-03-09 09:06:58 -07:00