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Documentation Index

Fetch the complete documentation index at: https://docs.letmepost.dev/llms.txt

Use this file to discover all available pages before exploring further.

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What it checks

For images: mimeType === "image/jpeg". JPEG only, no exceptions. For videos: mimeType ∈ { video/mp4, video/quicktime }. The mime is sniffed from the resolved bytes, not trusted from the file extension.

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Why JPEG-only for images

Meta’s Instagram container endpoint will accept a image/png URL but produces a code 100, error subcode 2207003 (or similar) at container creation time. Same for WebP, HEIC, GIF. The only mime IG actually publishes through the photo path is JPEG. Catching this locally with a clear rule + remediation saves you the round-trip and the opaque error.

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Failure response

{
  "error": {
    "code": "preflight_failed",
    "rule": "instagram.media.mime_allowed",
    "platform": "instagram",
    "message": "Image mime 'image/png' is not accepted by Instagram (JPEG only).",
    "remediation": "Re-encode to JPEG. Instagram's container endpoint rejects PNG, WebP, HEIC, and GIF on the photo path."
  }
}

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Remediation

Re-encode to JPEG: 
# ImageMagick
magick input.png -quality 85 output.jpg

# sharp (Node)
await sharp(input).jpeg({ quality: 85 }).toFile("output.jpg");
If your asset is a transparent PNG, IG won’t render the transparency anyway — flatten onto a background of your choice. For videos, re-encode to mp4 with H.264 + AAC (the codec subset IG accepts inside an mp4 container): 
ffmpeg -i input.mov -c:v libx264 -c:a aac -movflags +faststart output.mp4

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Upstream documentation

The 2207003 / 2207004 subcode family is undocumented in Meta’s developer docs but consistently observable. The empirical mapping is what we encode.