# How does FCPXML represent a split edit (audioStart / audioDuration), on which elements, in which units, and does the OTIO FCPX adapter read it?

- id: art_01M5MV5SHG6HKYZWRMCP2CQ2B9
- 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, T13 · tags: none
- updated: 2026-10-23T16:58:14.442Z
- url: https://veyrul.com/articles/art_01M5MV5SHG6HKYZWRMCP2CQ2B9

Apple's FCPXML DTD (1.7 archive and the 1.10 page) declares optional audioStart and audioDuration time attributes on clip, mc-clip, ref-clip, sync-clip and asset-clip and says they define J/L cuts (split edits) on composite A/V clips; times are rational seconds. Two FCPXML 1.11 files in a third-party Swift library contain the attribute pair on sync-clips, with audioStart equal to start and audioDuration shorter than duration. The OTIO FCPX adapter at c61839e1 never mentions either attribute and skips clip/sync-clip/mc-clip as items, so a split edit expressed this way is not read by it. The sign convention of audioStart relative to start and offset is not defined in the DTD text; a third-party importer treats any difference between audioStart/audioDuration and start/duration as a split edit and then follows the video timing.

Apple's FCPXML DTD (1.7 archive and the 1.10 page) declares optional audioStart and audioDuration time attributes on clip, mc-clip, ref-clip, sync-clip and asset-clip and says they define J/L cuts (split edits) on composite A/V clips; times are rational seconds. Two FCPXML 1.11 files in a third-party Swift library contain the attribute pair on sync-clips, with audioStart equal to start and audioDuration shorter than duration. The OTIO FCPX adapter at c61839e1 never mentions either attribute and skips clip/sync-clip/mc-clip as items, so a split edit expressed this way is not read by it. The sign convention of audioStart relative to start and offset is not defined in the DTD text; a third-party importer treats any difference between audioStart/audioDuration and start/duration as a split edit and then follows the video timing.

Curator qualifications: All quoted excerpts located; audioStart/audioDuration on clip, mc-clip, ref-clip, sync-clip and asset-clip define J/L cuts in rational seconds.

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

```json
{
  "citations": [
    {
      "url": "https://developer.apple.com/documentation/professional-video-applications/document-type-definition",
      "note": "candidate evidence excerpts"
    },
    {
      "url": "https://developer.apple.com/library/archive/documentation/Miscellaneous/Conceptual/LegacyDTDsFinalCutPro/FCPXMLDTDv1.7/FCPXMLDTDv1.7.html",
      "note": "candidate evidence excerpts"
    },
    {
      "url": "https://github.com/orchetect/swift-fcpxml/blob/00bcacf213cca9b99ced1efd3aad7529396719c7/Sources/SwiftFCPXML/Model/Protocols/Story%20Elements/FCPXMLElementAudioStartAndDuration.swift",
      "note": "candidate evidence excerpts"
    },
    {
      "url": "https://github.com/orchetect/swift-fcpxml/blob/00bcacf213cca9b99ced1efd3aad7529396719c7/Tests/SwiftFCPXMLTests/TestResource/FCPXML%20Exports/Occlusion3.fcpxml",
      "note": "candidate evidence excerpts"
    },
    {
      "url": "https://github.com/orchetect/swift-fcpxml/blob/00bcacf213cca9b99ced1efd3aad7529396719c7/Tests/SwiftFCPXMLTests/TestResource/FCPXML%20Exports/SyncClipRoles.fcpxml",
      "note": "candidate evidence excerpts"
    },
    {
      "url": "https://github.com/OpenTimelineIO/otio-fcpx-xml-adapter/blob/c61839e105fb035589d3ec704b1266a22089b425/src/otio_fcpx_xml_adapter/fcpx_xml.py",
      "note": "candidate evidence excerpts"
    },
    {
      "url": "https://github.com/OpenTimelineIO/otio-fcpx-xml-adapter/blob/c61839e105fb035589d3ec704b1266a22089b425/README.md",
      "note": "candidate evidence excerpts"
    },
    {
      "url": "https://developer.apple.com/documentation/professional-video-applications/asset-clip",
      "note": "candidate evidence excerpts"
    },
    {
      "url": "https://github.com/0xsline/OpenChatCut/blob/7fa4b7903e7ebecf832a36249f0c0c755200cc17/src/agent/tools/timeline-import-fcpxml-walk.ts",
      "note": "candidate evidence excerpts"
    },
    {
      "url": "https://github.com/0xsline/OpenChatCut/blob/7fa4b7903e7ebecf832a36249f0c0c755200cc17/src/agent/tools/timeline-import-fcpxml.verify.ts",
      "note": "candidate evidence excerpts"
    }
  ]
}
```

Evidence claims:
- [sourced_fact] Apple's FCPXML DTD (1.7 archive and the 1.10 page) declares optional audioStart and audioDuration time attributes on clip, mc-clip, ref-clip, sync-clip and asset-clip and says they define J/L cuts (split edits) on composite A/V clips; times are rational seconds. Two FCPXML 1.11 files in a third-party Swift library contain the attribute pair on sync-clips, with audioStart equal to start and audioDuration shorter than duration. The OTIO FCPX adapter at c61839e1 never mentions either attribute and skips clip/sync-clip/mc-clip as items, so a split edit expressed this way is not read by it. The sign convention of audioStart relative to start and offset is not defined in the DTD text; a third-party importer treats any difference between audioStart/audioDuration and start/duration as a split edit and then follows the video timing. · locator: candidate evidence excerpts · source: https://developer.apple.com/documentation/professional-video-applications/document-type-definition

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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