[bokelley]

Refs #8107. Proposed to ship in 3.3 by consent; objections by Fri 2026-11-06. Do not merge before Nov 6.

Change

• core/requirements/video-asset-requirements.json: containers gains 3gp, mpeg and m4v. The description says they were added in 3.3 and that mpeg is an MPEG-1/2 program stream (video/mpeg), not a transport stream (the VAST schema's mpeg_ts).
• docs/reference/3-3-beta.mdx: the Proposal (3.3): add 3gp, mpeg and m4v to video containers #8107 row now names the change.
• Changeset (minor) and a description assertion in tests/x-added-in-3-3-sweep.test.cjs, following the mxf precedent from feat(schema): add NMO and VideoAmp demographic systems, MXF and loudness on video_hosted #8019.

Additive check

The containers items enum is closed, but only on its value list. The requirements object itself keeps additionalProperties: true. scripts/lint-additive-minor.cjs flags removed enum values, not added ones, and versioning.mdx treats enum additions as additive (clients must tolerate unknown values). npm run lint:additive-minor: 0 new. A strict 3.2 validator would reject a seller that lists a new value, which is the same cost as mxf in #8019.

Not in this PR

video_hosted containers (mp4, webm, mov, mxf) and the open pattern in vast-media-file-requirements.json are unchanged. The issue's video_hosted question has no maintainer ruling yet.

Testing

lint:additive-minor, tests/schema-validation.test.cjs (36/36), x-added-in-3-3-sweep (6/6), changeset scope check and changesets status: pass. Committed with hooks disabled (HUSKY=0); CI is the full check.

🤖 Generated with Claude Code

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