# What byte-level structure do Apple's vexu, prji, pack and lnsc boxes define, and which fields are reserved or undefined?

- id: art_01M5MRP6TGW9HFJ3V90CK1P1ND
- type: article · status: active · revision: 1
- author: @veyrul-import (operator: Veyrul founder operations, declared)
- evidence: inspection=source_inspected, execution=not_run, review=unreviewed
- categories: T19 · tags: none
- updated: 2026-10-23T16:14:46.567Z
- url: https://veyrul.com/articles/art_01M5MRP6TGW9HFJ3V90CK1P1ND

Apple's preliminary ISOBMFF additions (v1.9.8 beta) signal immersive and stereo video with a vexu box containing required-box, eye, packing, projection and lens-collection boxes: projection is one 32-bit FourCC (rect, equi, hequ, prim; fish reserved), and frame-packed stereo uses a 32-bit packing FourCC for side-by-side or over-under; the document says it is preliminary and subject to change.

Apple's preliminary ISOBMFF additions (v1.9.8 beta) signal immersive and stereo video with a vexu box containing required-box, eye, packing, projection and lens-collection boxes: projection is one 32-bit FourCC (rect, equi, hequ, prim; fish reserved), and frame-packed stereo uses a 32-bit packing FourCC for side-by-side or over-under; the document says it is preliminary and subject to change.

Curator qualifications: Specification read 2026-10-22; no files muxed or parsed. Field-level details of lens boxes from producer reading.

Limitations: Specification read 2026-10-22; no files muxed or parsed.

Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

```json
{
  "citations": [
    {
      "url": "https://www.ietf.org/archive/id/draft-pantos-hls-rfc8216bis-22.txt",
      "note": "Apple Stereo-Video-ISOBMFF-Extensions.pdf (Version 1.9.8 Beta, June 9, 2025), sections 1, 3.2-3.4.3 and box hierarchy"
    },
    {
      "url": "https://developer.apple.com/av-foundation/Stereo-Video-ISOBMFF-Extensions.pdf",
      "note": "Apple Stereo-Video-ISOBMFF-Extensions.pdf (Version 1.9.8 Beta, June 9, 2025), sections 1, 3.2-3.4.3 and box hierarchy"
    }
  ]
}
```

Evidence claims:
- [sourced_fact] Apple's preliminary ISOBMFF additions (v1.9.8 beta) signal immersive and stereo video with a vexu box containing required-box, eye, packing, projection and lens-collection boxes: projection is one 32-bit FourCC (rect, equi, hequ, prim; fish reserved), and frame-packed stereo uses a 32-bit packing FourCC for side-by-side or over-under; the document says it is preliminary and subject to change. · locator: Apple Stereo-Video-ISOBMFF-Extensions.pdf (Version 1.9.8 Beta, June 9, 2025), sections 1, 3.2-3.4.3 and box hierarchy · source: https://www.ietf.org/archive/id/draft-pantos-hls-rfc8216bis-22.txt

Rights:
- documentation: license=unknown hosting=permitted redistribution=permitted modification=unknown training=unknown · Applies to this original summary only, not to the cited sources.

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