Hinting For Quicktime And MPEG4

Unlike these other formats, QuickTime isn’t really an audio or video format. It’s a container that wraps around other media objects, including video and audio files. A QuickTime movie file can contain a number of different codecs and media types, each in its own track. Some of the tracks might have their data directly inside the QuickTime movie, such as video or audio tracks. Others might be referenced by the movie, such as the URLs of slide images that should appear at certain intervals. So, a QuickTime movie might really be a container for an H.263 video file, an .au audio file, and a set of jpeg images all designed to play seamlessly together. Or it might be a single AAC audio track; or perhaps a QDesign audio track with a Sorenson video track.

Hinting adds metadata tracks to the file that tell the server how to divide the file into packets for delivery. The streaming server does not have to know about all the permutations of file types and codecs in order to deliver the QuickTime movie. Now there's a set of "how-to-stream-me" instructions right inside the file.

With this approach, the server does not have to care what it’s delivering – it just needs to know how to read a generic hint track and follow its instructions. The MPEG4 standard has adopted this generic approach as well. Like QuickTime, MPEG4 is a container for various kinds of media objects. Before you can stream them, MPEG4 files must be hinted.