Image Transformation

The /m/:key path serves media files from the CDN. For images, you can request on-the-fly resizing and format conversion.

Base URL

Media is served from https://cdn.atiru.io by default. If you configured a custom CDN, use your public_url_base instead.

Path: GET /m/:key

The :key is the file's file_id from the upload response.

Query parameters (images only)

Parameter	Description	Max value
width	Resize to this width (pixels). Aspect ratio preserved if height is omitted.	2000
height	Resize to this height (pixels). Aspect ratio preserved if width is omitted.	2000
format	Output format. One of: webp, avif, png, jpeg	-

You can combine parameters: ?width=200&height=200&format=webp

Examples

Original image (no transformation)

https://cdn.atiru.io/m/abc123

Resize to 200px width (height auto)

https://cdn.atiru.io/m/abc123?width=200

Resize to 200x200 thumbnail

https://cdn.atiru.io/m/abc123?width=200&height=200

Convert to WebP

https://cdn.atiru.io/m/abc123?format=webp

Thumbnail in WebP

https://cdn.atiru.io/m/abc123?width=100&height=100&format=webp

HTML

<!-- Original -->
<img src="https://cdn.atiru.io/m/abc123" alt="My image" />

<!-- Thumbnail -->
<img src="https://cdn.atiru.io/m/abc123?width=200&height=200" alt="Thumbnail" />

<!-- Responsive with WebP -->
<img
  src="https://cdn.atiru.io/m/abc123?width=400&format=webp"
  srcset="
    https://cdn.atiru.io/m/abc123?width=400&format=webp 400w,
    https://cdn.atiru.io/m/abc123?width=800&format=webp 800w
  "
  alt="Responsive image"
/>

curl

curl -o thumbnail.png "https://cdn.atiru.io/m/abc123?width=200&height=200&format=png"

Passthrough types (no transformation)

These file types are served as-is on /m/:key—no resize or format conversion:

• Video: video/mp4, video/webm, video/ogg, etc.
• Audio: audio/mpeg, audio/wav, audio/ogg, etc.
• PDF: application/pdf
• Fonts: font/woff, font/woff2, font/ttf, etc.

Query parameters (width, height, format) are ignored for these types.

Caching

Responses include Cache-Control: public, max-age=31536000 (1 year). CDNs can cache aggressively for fast delivery.

Limits

• Max dimension: 2000 pixels for width and height
• Rate limiting: See Rate Limiting. Image requests with resize/format may return 503 when the server is busy—retry with Retry-After header.