Intent to prototype : Matroska playback support

[Alastor Wu]

Summary:

Matroska (MKV) is a modern, flexible multimedia container format widely used by media enthusiasts and in open-source communities. It is capable of holding video, audio, and subtitles in a single file, similar to MP4, but with broader codec support. 

We propose prototyping Matroska support in Gecko for the following reasons:

• Compatibility and demand: Chromium-based browsers already support MKV playback. The lack of native support in Gecko results in playback failures, forced downloads instead of direct play, and the need for manual transcoding. Many users have requested first-class MKV playback.

• Standards-backed: Matroska (and EBML) are now published as IETF RFCs via the CELLAR working group, providing an open and stable specification that ensures long-term interoperability.

Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1422891

Specification: https://www.rfc-editor.org/info/rfc9559

Platform coverage: All 

Other browsers:
Blink (Chromium): Supported with common codecs such as H.264, AAC, Opus, and Vorbis, etc.
WebKit (Safari): Not supported.

[Tom Ritter]

I've read the Tech Brief [0], but it doesn't contain any
implementation details. I think this should get a security review
from Firefox Security Reviews <secr...@mozilla.com> . Some
questions that immediately come to mind that would be discussed in
that would be what third party libraries will be added to do this and
what processes will the new code be running in.

-tom

[0] https://docs.google.com/document/d/1SH5Pm1nRj9Qci9fBYVyE-5asj-GffL5evJa7OEZv3eY/edit?tab=t.0#heading=h.tfv43swtn2zr

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[Alastor Wu]

We don’t need any new third-party libraries. The demuxing will still be handled by nestegg, which we already use for WebM. We will extend it to support Matroska as well. The demuxing process itself remains unchanged and will continue to run in the content process, as it does now.

t...@mozilla.com 在 2025年9月2日 星期二清晨7:23:51 [UTC-7] 的信中寫道：