Amp-wp: Not all .gif files are animated

[mjangda]

We wrap any files ending in .gif in amp-anim but the GIF format supports more than just animated images. It would be nice to handle these cases.

[westonruter]

the GIF format supports more than just animated images

Such as a non-animated transparent GIF? What else would there be to support?

To detect whether or not a GIF is animated, this may depend on a core patch, such as 28474.2.diff. We'd then probably need to cache whether it is animated in _wp_attachment_metadata postmeta.

[westonruter]

We should re-open this when https://core.trac.wordpress.org/ticket/28474 is landed in core.