Changes

APNG is designed to allow incremental display of frames before the entire image has been read. This implies that some errors may not be detected until partway through the animation. It is strongly recommended that when an error is encountered decoders should discard all subsequent frames, stop the animation, and revert to displaying the placeholder image if possible. An error may be displayed to the user if appropriate.

APNG viewers Decoders must abandon the APNG chunks in a datastream with treat out-of-order APNG chunks and display the placeholder imageas an error. APNG-aware PNG editors should restore them to correct order using the sequence numbers.