Splitting APNG into png images with PHP

Question

I have a php code that splits an animated PNG image (APNG) into frames, but there is some kind of error. The images that are created by the function are not valid (PHP does not

Answer 1

The CRC needs to be recomputed when you change a chunk name from fdAT to IDAT, and remove 4 data bytes, to account for the new chunk name and data.