Icon - Images that show up on the map and in lists. What a player sees before drilling down. Icons are small, square images.
Media - May be an image, audio or video. Shows up in the objects themselves, when a player does drill down.
Referenced - Players can also render media through the use of HTML and Javascript, where they call this media from urls and choose how to render it through the code they write.
Formats: jpeg, gif (ARIS will animate these, even on the map!), png.
Sizes: < 2MB. In practice you want to optimize pixels heavily so your content loads over poor connections. You will be way under this limit. In general, just don't upload images directly from your 12 megapixel camera.
Plaques: Images are top-aligned (under the title), and will scale to fit the width of the screen (640 pixels). If you use a smaller image, it will get enlarged to fit this width, and there's no point using an image wider than 640 pixels.
Items: Images are centered horizontally and vertically. Images will initially be zoomed to fit in 640(w)x???(h), but they can be pinched to zoom in further (even animated gifs!) so large resolution images can be used in items.
Conversations: Like plaques, images are top-aligned (under the title), and will scale to fit the width of the screen (640 pixels). But the text of the conversation (lines and choices) covers some of the image (with some transparency). This amount depends on the amount of text in the conversation and the conversation text can be closed like a drawer (tap the ellipses). At maximum, the image height is ??? pixels.
Format: Any video iOS can play. Video is tricky. For a start, file type endings don't mean much. H.264 mp4 is the basic codec you want. But even with the right codec, it is possible to mess with the specifics enough in an attempt to optimize the file that the video doesn't end up playing on iOS.
Size: ARIS will accept videos up to 10MB. If you need something larger, consider linking the url (to YouTube for example) in the text content in ARIS, sending the player to see the video in a web view.
Pixel dimensions are nominally the same as for images, but videos are huge. You may want to use smaller pixel dimensions to reduce file size. Also optimize by reducing the audio bitrate and switching to mono sound.
Example: Many of my videos are 160(w)x120(h) with a mono audio bitrate of 32kbps.
Most places in ARIS where largish amounts of text can be entered and displayed to the player are also capable of rendering HTML and Javascript. This means code like the following can be used to include media in your objects in more flexible ways.
<audio autoplay loop><source src="http://arisgames.org/server/gamedatav2/10950/aris940d74d20534c562c6903f8ca65bce47.m4a"></audio>If you put this code in to a plaque for example, along with whatever you wanted the plaque to read, when the player viewed the plaque, they would hear this audio clip in the background as well (on a loop).