Hi,
In studying the x264 encoding guide ("http://www.avidemux.org/admWiki/doku.php?id=tutorial:h.264") it is noted that some settings (e.g. Psy RDO) are said to be good for "real life" videos but not for "animations".
However, recent productions of animes can also be rich in textures, it is then interesting how Avidemux classifies the inputs.
Is there a practical definition of animation ?
Avidemux doesn't classify the input whatsoever, the x264 plugin GUI reimplements / exposes features provided by libx264. Usually, animation implies large areas not changing between pictures, with less texture than in other types of content but with accented, contrast-rich borders of objects. Of course, a lot of works of animation artists doesn't fit into this stereotype.
Please be aware that the Wiki is in large parts extremely outdated and mostly obsolete (the x264 article still seems to offer a lot of useful background information, despite being 10 years old).