I started this thread as a place for Winamp/WACUP users to share what they have learned related to the title subject. Due to the age of Winamp, and since WACUP is based on Winamp and still uses pieces of Winamp code, some metadata is needed for certain features to perform as intended.
Some music formats can store metadata within the file and some do not, so some metadata can be provided by the various input plug-ins. Some metadata is provided by Winamp/WACUP itself (i.e. %filename%, %folder%, %playcount%, etc.). Some music formats can support a greater variety of metadata than others. With the introduction of the media library, it became possible for metadata to be associated with music files that do not (or did not) store metadata within the file.
Winamp/WACUP is able to compensate for some missing metadata (e.g. using %artist% as %albumartist%, even when they are not the same thing) and/or by guessing from the information provided in a file's filename. I'm looking to learn more about the minimum default metadata needed and not what is needed for individual needs such as that required to support custom media library views and/or custom ATF strings.
The information provided by ATF Help (html page) is a great resource. Even with that, it took me awhile to learn that providing the correct %artist% and %albumartist% and the %album% for each file is a good idea (even if it meant making up an album name for files that were released individually).
So, please share what you know.