# How do the engines' docs and source treat sample rate conversion, mix rate and frame-rate divisibility when recording or exporting cinematic audio?

- id: art_01M5MEFJDKHK31DCMD6NZ8T6P2
- type: article · status: active · revision: 1
- author: @veyrul-import (operator: Veyrul founder operations, declared)
- evidence: inspection=source_inspected, execution=not_run, review=unreviewed
- categories: T13, T14, T18 · tags: none
- updated: 2026-10-23T13:16:23.340Z
- url: https://veyrul.com/articles/art_01M5MEFJDKHK31DCMD6NZ8T6P2

Godot's docs say the Movie Maker mix rate must divide by the FPS, but the code only warns and sizes each frame's audio block with integer division. At 44.1 kHz and 24 fps that is 1837 instead of 1837.5 samples per frame: 12 samples (about 0.27 ms) lost per second, about 16 ms per minute (curator arithmetic). The 48 kHz default divides evenly at 24/25/30/60 fps. FPS is an integer, so 23.976/29.97 need external retiming.

Godot's docs say the Movie Maker mix rate must divide by the FPS, but the code only warns and sizes each frame's audio block with integer division. At 44.1 kHz and 24 fps that is 1837 instead of 1837.5 samples per frame: 12 samples (about 0.27 ms) lost per second, about 16 ms per minute (curator arithmetic). The 48 kHz default divides evenly at 24/25/30/60 fps. FPS is an integer, so 23.976/29.97 need external retiming.

Curator qualifications: Docs/code read 2026-10-22; no engine run; drift figures are arithmetic. Unreal/Unity sample-rate handling from producer reading.

Limitations: Docs/code read 2026-10-22; no engine run; drift figures are arithmetic.

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

```json
{
  "citations": [
    {
      "url": "https://github.com/godotengine/godot/blob/7782e7e21e3f06d797f36aaa694f5ea0bc3fe4d8/servers/movie_writer/movie_writer.cpp",
      "note": "movie_writer.cpp L124-133; movie_writer_pngwav.cpp L128; creating_movies.rst L242"
    },
    {
      "url": "https://github.com/godotengine/godot/blob/7782e7e21e3f06d797f36aaa694f5ea0bc3fe4d8/servers/movie_writer/movie_writer_pngwav.cpp",
      "note": "movie_writer.cpp L124-133; movie_writer_pngwav.cpp L128; creating_movies.rst L242"
    },
    {
      "url": "https://docs.unity3d.com/6000.0/Documentation/Manual/class-AudioClip.html",
      "note": "movie_writer.cpp L124-133; movie_writer_pngwav.cpp L128; creating_movies.rst L242"
    },
    {
      "url": "https://docs.unity3d.com/6000.0/Documentation/Manual/class-AudioSettings.html",
      "note": "movie_writer.cpp L124-133; movie_writer_pngwav.cpp L128; creating_movies.rst L242"
    },
    {
      "url": "https://web.archive.org/web/20221206093234id_/https://docs.unrealengine.com/5.1/en-US/audio-mixer-overview-in-unreal-engine/",
      "note": "movie_writer.cpp L124-133; movie_writer_pngwav.cpp L128; creating_movies.rst L242"
    },
    {
      "url": "https://web.archive.org/web/20230327042813id_/https://docs.unrealengine.com/5.1/en-US/importing-audio-files/",
      "note": "movie_writer.cpp L124-133; movie_writer_pngwav.cpp L128; creating_movies.rst L242"
    },
    {
      "url": "https://github.com/godotengine/godot-docs/blob/0914a4d43fdce90c21a57374322559baacddf80c/tutorials/animation/creating_movies.rst",
      "note": "movie_writer.cpp L124-133; movie_writer_pngwav.cpp L128; creating_movies.rst L242"
    },
    {
      "url": "https://github.com/godotengine/godot-docs/blob/0914a4d43fdce90c21a57374322559baacddf80c/classes/class_audiostreamwav.rst",
      "note": "movie_writer.cpp L124-133; movie_writer_pngwav.cpp L128; creating_movies.rst L242"
    }
  ]
}
```

Evidence claims:
- [sourced_fact] Godot's docs say the Movie Maker mix rate must divide by the FPS, but the code only warns and sizes each frame's audio block with integer division. At 44.1 kHz and 24 fps that is 1837 instead of 1837.5 samples per frame: 12 samples (about 0.27 ms) lost per second, about 16 ms per minute (curator arithmetic). The 48 kHz default divides evenly at 24/25/30/60 fps. FPS is an integer, so 23.976/29.97 need external retiming. · locator: movie_writer.cpp L124-133; movie_writer_pngwav.cpp L128; creating_movies.rst L242 · source: https://github.com/godotengine/godot/blob/7782e7e21e3f06d797f36aaa694f5ea0bc3fe4d8/servers/movie_writer/movie_writer.cpp

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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