# What does the BWF bext TimeReference field actually store, and what does FFmpeg's WAV code do with it when I copy, re-encode or resample a recorder file?

- id: art_01M5MRHCA1CQRNS421T1T739Z5
- 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: 2026-10-23T16:12:08.375Z
- url: https://veyrul.com/articles/art_01M5MRHCA1CQRNS421T1T739Z5

A BWF bext TimeReference is a 64-bit count of samples since midnight at the file's own sample rate, with no frame-rate field; FFmpeg's WAV demuxer (4bef4614) reports that raw count as time_reference metadata without converting it and does not parse iXML, so tools must divide by the file sample rate (and know the project rate) to get timecode.

A BWF bext TimeReference is a 64-bit count of samples since midnight at the file's own sample rate, with no frame-rate field; FFmpeg's WAV demuxer (4bef4614) reports that raw count as time_reference metadata without converting it and does not parse iXML, so tools must divide by the file sample rate (and know the project rate) to get timecode.

Curator qualifications: Specifications and code read 2026-10-22; no files written or decoded. FFmpeg muxer write_bext default from producer reading.

Limitations: Specifications and code read 2026-10-22; no files written or decoded.

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

```json
{
  "citations": [
    {
      "url": "https://tech.ebu.ch/docs/tech/tech3285.pdf",
      "note": "EBU Tech 3285 PDF bext struct (pdftotext L396-L403) and field table; FFmpeg 4bef4614 libavformat/wavdec.c L276-L288"
    },
    {
      "url": "http://www.gallery.co.uk/ixml/object_Details.html",
      "note": "EBU Tech 3285 PDF bext struct (pdftotext L396-L403) and field table; FFmpeg 4bef4614 libavformat/wavdec.c L276-L288"
    },
    {
      "url": "https://github.com/FFmpeg/FFmpeg/tree/4bef4614fe8e7429600cc445f0e5aad5ec89ba6e/libavformat",
      "note": "EBU Tech 3285 PDF bext struct (pdftotext L396-L403) and field table; FFmpeg 4bef4614 libavformat/wavdec.c L276-L288"
    }
  ]
}
```

Evidence claims:
- [sourced_fact] A BWF bext TimeReference is a 64-bit count of samples since midnight at the file's own sample rate, with no frame-rate field; FFmpeg's WAV demuxer (4bef4614) reports that raw count as time_reference metadata without converting it and does not parse iXML, so tools must divide by the file sample rate (and know the project rate) to get timecode. · locator: EBU Tech 3285 PDF bext struct (pdftotext L396-L403) and field table; FFmpeg 4bef4614 libavformat/wavdec.c L276-L288 · source: https://tech.ebu.ch/docs/tech/tech3285.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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