Check if file is apng

[PringlePot]

It would be nice if theres a simple function to check if a file is actually an apng?

[kettek]

This should be possible by creating a new function that only searched to see if the acTL chunk exists. I'll look into the most idiomatic way to present this.

[schainks]

My 0.02 on this is looking for acTL is the idiomatic way, as it is part of the standard. If the PNG Is animated, acTL chunk must exist: https://wiki.mozilla.org/APNG_Specification#.60acTL.60:_The_Animation_Control_Chunk

[kettek]

Would need a helper func to scan only as far as acTL or until first IDAT. We could, as a convenience, return the acTL information if it exists as well. Perhaps vaguely like:

func CheckAPNG() (isAnimation bool, frameCount int, playCount int)

[kettek]

It is probably unnecessary to have the above convenience function, as the end-user can actually extract the data if they need more information. I believe isAPNG() bool or isAnimated() bool would suffice.

[schainks]

This implementation in JS looks like it does what you describe in terms of scanning for the chunk, then returning immediately: https://github.com/qzb/is-animated/blob/master/lib/types/png.js