fix(avatar): freeze APNG and animated WebP avatars, not just GIF#772
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The freeze decided "is this animated?" from the declared MIME type (blob.type === 'image/gif'). That misses the common real-world cases: many animated avatars are APNG or animated WebP, and the SDK occupant-avatar path stores avatars as image/png regardless of the real format (Profile.ts), so even a GIF can arrive mistyped. Those avatars were never frozen and played continuously (kuyuhi in #XSF is an animated PNG). Detect animation from the actual image bytes instead: GIF header, APNG acTL control chunk, or animated-WebP ANIM chunk. The canvas first-frame extraction already handles any decodable raster format, so the freeze now covers all three. Static JPEG/PNG/WebP are untouched (no signature match).
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Summary
Follow-up to #770. Animated avatars are meant to show a frozen first frame and play only on hover. #770 fixed the freeze-frame cache for virtualized scrolling, but the freeze still only ever applied to literal GIFs.
The decision "is this animated?" was made from the declared MIME type (
blob.type === 'image/gif'). That misses the common real-world cases:<img>.image/pngregardless of the real format (Profile.tshardcodes it for PEP avatars and defaults to it for vCard avatars with no<TYPE>), so even a GIF can arrive mistyped.So these avatars were never frozen and animated continuously (observed: kuyuhi in #XSF, an animated PNG).
This detects animation from the actual image bytes instead of the declared type: GIF header, APNG
acTLcontrol chunk, or animated-WebPANIMchunk. The existing canvas first-frame extraction already handles any decodable raster format, so the freeze now covers all three. Static JPEG/PNG/WebP are left untouched (no signature match), so there is no extra work for the common case.Known gap
Animated AVIF/HEIF are not detected (rare as avatars, and WebKit animation support for them is limited). They would keep animating.