MNG was unfortunately designed so badly that Mozilla had to create APNG to replace it. In retrospect, MNG was only capable to do about 10% of what SVG 1.0 can do on top of an incomprensible binary format. (One may argue that SVG is also badly designed for this reason.)
yeah I remember no joy working with implementations of it. The whole thing smelt like a standards body mess when really they should have got one good engineer to just make something workable in a weekend. Its possibly worse than the OpenGLES mess.
Okay, I admit the "badly designed" part is my claim, but I'm very confident in that claim and can explain why.
The original impetus that led to MNG was animated GIF. While GIF was also designed as extensible, GIF practically only had a handful number of extensions and wasn't that complex. MNG in comparison was essentially a binary version of SVG as I have described, except that it had no vector graphics and can more accurately be described as a binary slideshow format [1]. No one asked for this! The PNG development group forgot its goal and made a much bloated specification. As a result libmng, while working, was a quite big library to be incorporated into Gecko and ultimately rejected in favor of APNG which only required a small patch to libpng. It is amusing that the original PNG specification had chunks corresponding to GIF extensions including animation one; those chunks might have been widespread in the alternate universe!
If the group's goal was indeed a slideshow format, it should have been two separate formats, one for multi-part images and one for animations and object transformations. The former is necessary because one aspect of GIF was that a difference from the previous frame can be encoded, so this "Delta-PNG" format should have been made into the mainline PNG specification as an option. (These additional images could have been used as previews, for example.) And anything else should be a simple textual format that refers to external files. MNG instead had chunks for JPEG images---came with its standalone sister format called JNG---, which is absurd when you think about it---why should there be JNG when JFIF and Exif already exist? The modern SVG happens to be perfectly usable as this second format, and it is fine being textual.
