Detect animated images by sniffing file headers#2187
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Extension-based detection froze static GIFs and missed APNG distributed as .png, animated WebP and animated AVIF. When GIF autoplay is off, fetch the first 16 KB of the image (falling back to the HTTP proxy when CORS blocks the read) and inspect the container: NETSCAPE loop extension or a second image descriptor for GIF, an acTL chunk before IDAT for PNG, the VP8X animation flag for WebP and the avis brand for AVIF. Results are cached per URL and fall back to the extension-based presumption when undeterminable.
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| Status | Name | Latest Commit | Updated (UTC) |
|---|---|---|---|
| ❌ Deployment failed View logs |
nostter | 2d3a478 | Jun 10 2026, 11:25 PM |
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Extension-based detection froze static GIFs and missed APNG distributed
as .png, animated WebP and animated AVIF. When GIF autoplay is off,
fetch the first 16 KB of the image (falling back to the HTTP proxy when
CORS blocks the read) and inspect the container: NETSCAPE loop
extension or a second image descriptor for GIF, an acTL chunk before
IDAT for PNG, the VP8X animation flag for WebP and the avis brand for
AVIF. Results are cached per URL and fall back to the extension-based
presumption when undeterminable.