[Webkit-unassigned] [Bug 217897] New: [iOS 14] Animated WebP with transparency doesn't render properly

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=217897

            Bug ID: 217897
           Summary: [iOS 14] Animated WebP with transparency doesn't
                    render properly
           Product: WebKit
           Version: Safari 14
          Hardware: iPhone / iPad
                OS: Other
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Images
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: alanodaval at hotmail.com

Created attachment 411728

  --> https://bugs.webkit.org/attachment.cgi?id=411728&action=review

Video showing how the WebP display on other browsers (left) vs how it displays on iOS 14 (right)

Rendering for animated WebP with transparency doesn't seem to be working properly on iOS 14.

It doesn't seem to happen to every single image, WebP with no transparency and one example encoded lossless seem to work fine.

But both a sample I found in a stackoverflow question and other one my team prepared seem to show flickering in the background and bits of other frames.

This bug happens both in iOS emulators and actual devices.

I've tested this on other major browser vendors (Chromium, Gecko) and they both seem to work as expected (look at the left side of the attached video)


References: 
- A minimal reproduction I prepared; the video attached was recorded using it: https://animated-webp.glitch.me/
- The stackoverflow question: https://stackoverflow.com/questions/64259387/ios-14-webp-animation-flahes-with-a-white-background-in-safari-and-chrome

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