The Animated Portable Network Graphics file format was proposed in 2004, but failed to take off as a replacement for the animated GIF file format widely used to embed short animations online.
Unlike animated GIFs, APNG files support 24-bit images and 8-bit transparency not available for GIFs.
According to Wikipedia, the APNG file format also retains backward compatibility with non-animated PNG files so browsers that don’t feature support for APNGs can still render still images.
As MacRumors points out, Safari on iOS 8 is capable of animating APNGs. If you are reading this article using Safari on your iPhone, iPod touch or iPad, the APNG embedded bellow should animate.
Loading this webpage in any other browser, including Safari on non-Yosemite Macs, would only display the static image.
The PNG group rejected the proposed APNG specification back in 2007 due to the lack of support from major browser vendor. To this date, only Firefox has supported APNGs.
In addition to Safari on iOS 8, Safari on Yosemite has also been found to support APNGs.
As a reminder, all App Store apps use the embedded Safari engine
because Apple does not allow third-party frameworks for web content.