Changes

Each frame inherits every property specified by any critical or ancillary chunks before the first `IDAT` in the file, except the width and height, which come from the `fcTL` chunk.

If the PNG `pHYs` chunk is present, the APNG images and their `x_offset` and `y_offset` values must be scaled in the same way as the main image. Conceptually, such scaling occurs while mapping the output buffer onto the canvas.