Bug 248755

Animated AVIF rendering seems glitchy; images seem to be rendered inconsistently to the point where navigating to the same image and refreshing randomly results in different rendering. The WPT test at http://wpt.live/avif/animated-avif-timeout.html is failing in Safari because of this. This test uses an animated AVIF image with a single short red frame followed by a long green frame — just two colors in total. In Safari, even when accessing the image directly, it gets rendered as a short red frame followed by the expected dark green frame, randomly (& inconsistently) changing to a lighter shade of green. I’ve tested with various animated AVIF images and haven’t found a single one that renders interoperably with Chrome. I’ll attach some test images that I’ve used, attributing their sources here: 1) 1-red-then-green.avif is the WPT test image taken from http://wpt.live/images/animated-avif.avif. Its rendering is inconsistently glitchy on WebKit. (If not, try reloading the image.) 2) 2-google-noto-animated-emoji-1f604.avif is a random animation taken from https://googlefonts.github.io/noto-emoji-animation/. Its rendering is inconsistently glitchy on WebKit. (If not, try reloading the image.) 3) 3-sequence-without-pitm.avif is an AVIF with an image sequence but no primary item (no `pitm` box), taken from https://bugzilla.mozilla.org/show_bug.cgi?id=1686338#c6. Chrome displays this animation; WebKit just shows a static black rectangle. 4) 4-sequence-with-pitm.avif is an AVIF with an image sequence with a still image primary item (`pitm`), taken from https://bugzilla.mozilla.org/show_bug.cgi?id=1686338#c7. Its rendering is inconsistently glitchy on WebKit. (If not, try reloading the image.) I haven’t found an animated AVIF image that renders correctly. I’m using macOS Ventura 13.0.1 (22A400) and I’m testing in the latest Safari Technology Preview Release 159 (Safari 16.4, WebKit 18615.1.12.130.1).