108 Personal Content Experience: Managing Digital Life in the Mobile Age EXIF, then, is a standard for defi ning how to store image data and camera information in fi les, and applies to the actual data itself. EXIF information is embedded in the fi les along with the actual content. As can be seen from Figure 4-3, EXIF deals mostly with camera-based technical information, such as the use of fl ash, aperture size, and zoom level. A different approach was adopted by IIM/IPTC headers, which we discussed above. These image formats all largely lack some of the potential items of interest to the users, such as automatically entered context information. 4.6.7 Quicktime 39 The Quicktime multimedia architecture developed by Apple com- prises a rich set of conventions, fi le formats, APIs, and tools for creating, viewing, and editing multimedia content on personal computers. It has been mostly used for movies (famously for fi lm trailers and music videos), but allows synchronization, compositing, layering, and control of multiple kinds of media, including images, audio, text, sprites, live streams, synthesized music, VR, and others. While the Quicktime format is not specifi cally designed to convey arbitrary metadata about media fi les, its structure allows embedding any kind of metadata. A Quicktime “movie” consists of multiple tracks, which are often time-synchronized, each of which can contain multiple instances of a single media type with different characteristics. The format stores various kinds of metadata with each media segment, including dimensions, frame/sample rates, timescales, codecs, non- destructive edit lists, etc.. In effect, Quicktime playback consists of a real-time multitrack, multiformat, multimedia, re-synthesis process. Quicktime fi les are organized into hierarchical trees of “atoms”, that in turn refer to other atoms, until the leafs on the tree contain the elementary information, such as movie frames. Metadata is then stored within such atoms, as with any other content. The Quicktime APIs allow higher-level manipulation of the known metadata types. The fi le organization and object nesting relies on keeping track of object sizes as they are mapped into linear fi les. Quicktime supports nonlinear datatypes, such as “sprites”, which can be useful in allowing user control of playback, or to refer to exter- nal information in specifi c places in the movie (“Click the actress for her biography”). The Quicktime architecture achieves many desirable goals of a metadata architecture: it is extensible, transparent, effi cient, and it 39 http://developer.apple.com/quicktime/