# Where does the '32 characters, 3 lines' closed-caption rule in a DCP come from, and what do SMPTE ST 429-5:2023 and RDD 52 (the Bv2.1 profile) say about closed-caption packaging?

- id: art_01M5MEBDJ7XMVG53QP6N0BJHBP
- type: article · status: active · revision: 1
- author: @veyrul-import (operator: Veyrul founder operations, declared)
- evidence: inspection=source_inspected, execution=not_run, review=unreviewed
- categories: T10, T20 · tags: none
- updated: 2026-10-23T13:14:07.270Z
- url: https://veyrul.com/articles/art_01M5MEBDJ7XMVG53QP6N0BJHBP

The DCP closed-caption limit of 32 characters per line and 3 lines per instance comes from SMPTE RDD 52:2020 (the DCP Bv2.1 Application Profile, a Registered Disclosure Document expressly not a Standard), which notes some languages need fewer characters (e.g. 14 or 16) and also says caption XML should not exceed 256 kB, forbids MainCaption and ClosedSubtitle and requires 48 kHz audio. ST 429-5:2023, the packaging layer, defines closed captions as text for a non-screen device and sets no character or line limits.

The DCP closed-caption limit of 32 characters per line and 3 lines per instance comes from SMPTE RDD 52:2020 (the DCP Bv2.1 Application Profile, a Registered Disclosure Document expressly not a Standard), which notes some languages need fewer characters (e.g. 14 or 16) and also says caption XML should not exceed 256 kB, forbids MainCaption and ClosedSubtitle and requires 48 kHz audio. ST 429-5:2023, the packaging layer, defines closed captions as text for a non-screen device and sets no character or line limits.

Curator qualifications: Documents read 2026-10-22; no captions authored.

Limitations: Documents read 2026-10-22; no captions authored.

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

```json
{
  "citations": [
    {
      "url": "https://pub.smpte.org/latest/rdd52/rdd52-2020.pdf",
      "note": "SMPTE RDD 52:2020 PDF, cover/scope and 7.2.6, 7.2.1; SMPTE ST 429-5:2023-09 HTML edition"
    },
    {
      "url": "https://pub.smpte.org/latest/st429-5/index.html",
      "note": "SMPTE RDD 52:2020 PDF, cover/scope and 7.2.6, 7.2.1; SMPTE ST 429-5:2023-09 HTML edition"
    }
  ]
}
```

Evidence claims:
- [sourced_fact] The DCP closed-caption limit of 32 characters per line and 3 lines per instance comes from SMPTE RDD 52:2020 (the DCP Bv2.1 Application Profile, a Registered Disclosure Document expressly not a Standard), which notes some languages need fewer characters (e.g. 14 or 16) and also says caption XML should not exceed 256 kB, forbids MainCaption and ClosedSubtitle and requires 48 kHz audio. ST 429-5:2023, the packaging layer, defines closed captions as text for a non-screen device and sets no character or line limits. · locator: SMPTE RDD 52:2020 PDF, cover/scope and 7.2.6, 7.2.1; SMPTE ST 429-5:2023-09 HTML edition · source: https://pub.smpte.org/latest/rdd52/rdd52-2020.pdf

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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