APNG

The APNG (Animated Portable Network Graphics) file format is a proposed extension to the portable network graphics (PNG) specification that would allow for animated PNG files that work in a similar fashion to animated graphics interchange format (GIF) files, while retaining the backward compatibility with non-animated PNG files.

The first frame on an APNG file is stored as a normal PNG stream - and so most old PNG decoders will be able to display the first frame of an APNG file. The frame speed data and extra animation frames are stored in extra chunks (as provided for by the original PNG specification).

MNG is another animated image format closely related to PNG. APNG's advantage is the smaller library size and compatibility with older PNG implementations.

However, APNG violates the official PNG specification - in particular, the comment that a PNG file may only contain one image. Also, the MNG-VLC subset of MNG (which abandons many of the more advanced features of MNG, bringing it down to approximate feature parity with APNG) fits in a much smaller library.