Whoops, I've been trying to decide if I should make some adjustments to the nice new documentation, all the while missing the link to this thread. I've been working with Kodi and artwork for a bit and I have some suggestions for you. ... Good grief, sorry for the braindump; I do hope it's more useful than obnoxious.
- Animated artwork is a prickly pear
- Kodi doesn't cache animated artwork and will not play them (only displaying the first frame) unless they are stored on a local file system or accessed with a "special://" path, but not network shares configured in Kodi nor HTTP URLs. By local file system I mean directly attached to the device Kodi is running on, and perhaps also includes network shares mounted outside of Kodi.
- The usage convention for skins to display animated artwork is to use the artwork types 'animatedfanart' and 'animatedposter' (these are set by Skin Helper Service), and to match Kodi's file naming convention* they should be named 'animatedfanart.gif' and 'animatedposter.gif' or '<NameOfVideoFile>-animatedfanart.gif' and '<NameOfVideoFile>-animatedposter.gif'
- Giving them different art types allows skins to only use animated artwork in specific situations, rather than an all or nothing sort of deal. Imagine a view that shows a large focused poster and several other posters laid out to the side; animating all of those posters would probably give most of us a headache, best to display just one animated image for the focused item and keep the rest static.
- Kodi limits the size of animated artwork to roughly 12 frames of 1920x1080 (technically the limit is 11 frames but Kodi will decode full frames until it has decoded MORE than this limit). This limit is defined as fully decoded pixels, so no amount of GIF finagling or praying to the compression gods will give even a single pixel more. With the recommended size of 1000x1500 for posters, that leaves 16 frames, while the trend on the animated poster thread is for smaller images with more frames (a recent one is 500x713 with 60 frames). Kodi will discard any remaining frames after it has reached this limit, which will probably look bad when displayed, so this limit should be made clear.
- While the movie "thumb" image may have been the poster a long time ago, these days it is a separate and valid image type all its own, and it's an actual thumbnail from the/a video file itself, just like episodes. Most display problems caused by the existence of "thumb" images for movies is due to the fact that skins are still asking for "thumb" when they intend to display a poster.
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- Artwork Downloader creates extrathumbs out of resized 'backdrops' from The Movie Database for use as actual thumbnails, and while their usage seems rare in skins, I've still only ever seen skins using them as actual thumbnails rather than more posters.
- Kodi has zero support for creating or loading movie set artwork, so it's no help for a convention, but we have had one tool that imports them into Kodi for quite a long time: Movie Set Artwork Automator. The wiki links directly to it in the relevant sections at the bottom of the movie artwork page, but then suggests a different convention ("movieset-fanart.jpg" and poster stored in each movie's folder) that only seems to be supported by one other tool (TinyMediaManager), with no support for actually getting them into the Kodi library proper other than manually assigning them by hand. However, the MSAA convention of a central directory for movie set artwork is better supported, as TMM also supports it, plus Ember, another external media manager that also utilizes JSON-RPC to update Kodi's library without refreshing the item. In addition, the "movie set artwork in every movie directory" strategy comes with one big problem that the central directory avoids: duplicate artwork, or at least the potential for duplicate artwork, that makes managing this artwork much more difficult, for both software and folks that want to replace or manage images by hand.
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- I'm not sure TV show discs should be in the list. While TV shows often have discs of their own, these images haven't generally been used in Kodi, there are usually more than one disc per season so the list could get big, TV show discs are boring more often than movie discs, and they aren't readily available from an open API.
- Not obnoxious enough, ... yes.
* While Kodi will only import the small selection of basic artwork, it will export all artwork that has been cached, and it always uses the exact same artwork type in the filename that skins use to display them, which is just as simple and elegant and perfectly descriptive as Kodi's artwork support itself (it can get messy at the fringes, but mostly it's just great).
Edit: I will try to make these edits myself.
Edit 2: Some taken care of.