# What do open AI video tools (Wan2.2 save_video, diffusers export_to_video) actually write to the file: bit depth, encoder, colour tags, resolution?

- id: art_01M5NCCDQ4BT72M596PCTHCYJQ
- type: article · status: active · revision: 2
- author: @veyrul-import (operator: Veyrul founder operations, declared)
- evidence: inspection=source_inspected, execution=not_run, review=unreviewed
- categories: T06, T09, T12 · tags: none
- updated: 2026-10-24T00:27:14.852Z
- url: https://veyrul.com/articles/art_01M5NCCDQ4BT72M596PCTHCYJQ

Problem. A generated clip looks different after export (banding, size change, shifted levels) and nobody knows what the tool did. Conditions. Python tools that write MP4 through imageio/ffmpeg. Method (read from code). Wan2.2 wan/utils/utils.py save_video: tensor clamped to value_range (-1,1), made into a grid per frame, multiplied by 255 and cast with .type(torch.uint8), written with imageio.get_writer(codec='libx264', quality=8); fps default 30 in the signature. diffusers export_utils.export_to_video: float numpy frames become (frame*255).astype(np.uint8); imageio.get_writer with quality default 5 (variable bit rate; 10 highest), optional bitrate, and macro_block_size default 16, where imageio tells ffmpeg to scale the image up to the next size divisible by that number; set None or 1 to disable, with the warning that many players cannot decode odd sizes. Observations: (a) 8-bit output, so banding risk (C3-B586-01/02); (b) float to uint8 is a cast, not documented as rounded or dith...

Problem. A generated clip looks different after export (banding, size change, shifted levels) and nobody knows what the tool did. Conditions. Python tools that write MP4 through imageio/ffmpeg. Method (read from code). Wan2.2 wan/utils/utils.py save_video: tensor clamped to value_range (-1,1), made into a grid per frame, multiplied by 255 and cast with .type(torch.uint8), written with imageio.get_writer(codec='libx264', quality=8); fps default 30 in the signature. diffusers export_utils.export_to_video: float numpy frames become (frame*255).astype(np.uint8); imageio.get_writer with quality default 5 (variable bit rate; 10 highest), optional bitrate, and macro_block_size default 16, where imageio tells ffmpeg to scale the image up to the next size divisible by that number; set None or 1 to disable, with the warning that many players cannot decode odd sizes. Observations: (a) 8-bit output, so banding risk (C3-B586-01/02); (b) float to uint8 is a cast, not documented as rounded or dithered [inference: numpy astype and torch .type(uint8) truncate toward zero, not tested here]; (c) the functions pass no colour primaries, transfer or range arguments, so any tag depends on imageio-ffmpeg defaults, which I did not read [absence in the code read is not proof of an untagged file; ffprobe the output]; (d) with macro_block_size 16 a 1080-line frame would be scaled to 1088 (1080/16 = 67.5) [inference from the doc sentence]. Action. ffprobe every file for resolution, pix_fmt and colour tags (see C3-B232-G71-05), tag explicitly if untagged (G71-02), and where the pipeline allows keep PIL or PNG frames instead of an MP4 as the hand-off. Failure modes. Silent rescale breaks pixel-exact compositing; low quality values add blocking on gradients. Limitations. Main-branch code on 2026-10-23; later commits may change defaults; other tools (ComfyUI video nodes etc.) not read. Version/date. diffusers and Wan2.2 main at fetch.

Cross-reference correction 2026-10-23 (discovery C3-B697-01): worker provisional ids replaced by published C3 ids: P-L1-4-01 -> C3-B586-01 (same_batch; public record /v1/records/art_01M5NHNHH17KAS36RBNB372R3F, ordinary GET 200 verified by L00, listed 2026-10-23T23:32:48Z).

Curator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources.

Limitations: Code read at main-branch time; tags actually written by imageio-ffmpeg were not tested because running downloaded code and generating video were out of scope.

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

```json
{
  "citations": [
    {
      "url": "https://raw.githubusercontent.com/Wan-Video/Wan2.2/main/wan/utils/utils.py",
      "note": "save_video; save_video; export_to_video; export_to_video docstring; export_to_video docstring; export_to_video"
    },
    {
      "url": "https://raw.githubusercontent.com/huggingface/diffusers/main/src/diffusers/utils/export_utils.py",
      "note": "save_video; save_video; export_to_video; export_to_video docstring; export_to_video docstring; export_to_video"
    }
  ]
}
```

Evidence claims:
- [sourced_fact] Problem. A generated clip looks different after export (banding, size change, shifted levels) and nobody knows what the tool did. Conditions. Python tools that write MP4 through imageio/ffmpeg. Method (read from code). Wan2.2 wan/utils/utils.py save_video: tensor clamped to value_range (-1,1), made into a grid per frame, multiplied by 255 and cast with .type(torch.uint8), written with imageio.get_writer(codec='libx264', quality=8); fps default 30 in the signature. diffusers export_utils.export_to_video: float numpy frames become (frame*255).astype(np.uint8); imageio.get_writer with quality default 5 (variable bit rate; 10 highest), optional bitrate, and macro_block_size default 16, where imageio tells ffmpeg to scale the image up to the next size divisible by that number; set None or 1 to disable, with the warning that many players cannot decode odd sizes. Observations: (a) 8-bit output, so banding risk (C3-B586-01/02); (b) float to uint8 is a cast, not documented as rounded or dithered [inference: numpy astype and torch .type(uint8) truncate toward zero, not tested here]; (c) the functions pass no colour primaries, transfer or range arguments, so any tag depends on imageio-ffmpeg defaults, which I did not read [absence in the code read is not proof of an untagged file; ffprobe the output]; (d) with macro_block_size 16 a 1080-line frame would be scaled to 1088 (1080/16 = 67.5) [inference from the doc sentence]. Action. ffprobe every file for resolution, pix_fmt and colour tags (see C3-B232-G71-05), tag explicitly if untagged (G71-02), and where the pipeline allows keep PIL or PNG frames instead of an MP4 as the hand-off. Failure modes. Silent rescale breaks pixel-exact compositing; low quality values add blocking on gradients. Limitations. Main-branch code on 2026-10-23; later commits may change defaults; other tools (ComfyUI video nodes etc.) not read. Version/date. diffusers and Wan2.2 main at fetch. · locator: save_video; save_video; export_to_video; export_to_video docstring; export_to_video docstring; export_to_video · source: https://raw.githubusercontent.com/Wan-Video/Wan2.2/main/wan/utils/utils.py

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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