 (September 1999)(Disk 2).iso/Technical Publications/quicktime/qtdevdocs/images/qtsmban.gif){kind=small}
 (September 1999)(Disk 2).iso/Technical Publications/quicktime/qtdevdocs/images/qt4api.gif)
Road Map to QuickTime 4
A video digitizer component converts analog video input into a series of digital video images. It is extremely low-level software that talks directly to hardware. Most applications programs can obtain digitized video through a sequence grabber component, which provides a higher-level interface that shields the applications developer from the complexities of video digitizers. It is possible for an application to interact directly with a video digitizer, for greater control, but this is not recommended.
You do not need to read this chapter unless you plan to create a video digitizer component, or a piece of software that interacts with a video digitizer component directly. The sections describing video digitizers in general, and the new features of video digitizers since QuickTime 1.5, may be of general interest to QuickTime developers. Your application can define a custom interrupt function that will be called by the video digitizer component; if you plan to do this, read the section " Application-Defined Function ," below.
About Video Digitizer ComponentsInside Macintosh describes the general characteristics and capabilities of video digitizer components.
New Features of Video Digitizer ComponentsQuickTime 4 Reference describes the support for timecodes added to video digitizer components since QuickTime 1.5. Also new are functions for controlling compressed source devices, controlling digitization data rate and packet size, and retrieving the audio source associated with a video input; these features are documented in the "Functions" section of this chapter.
Using Video Digitizer ComponentsInside Macintosh describes how you can control a video digitizer component directly. Topics covered include telling the digitizer where to put converted video data, starting and stopping the digitizer, improving performance through multiple buffering, and finding the time of a frame capture without a timecode.
Inside Macintosh describes in detail how to create a video digitizer component. This will be of interest only to developers intending to create a video digitizer. The introduction to this section lists all the enumerators used as request codes for each function your component must support.
Inside Macintosh describes the functions a video digitizer must support, and those that it may optionally support. The functions are divided into groups that serve a common purpose. QuickTime 4 Reference describes the new functions added to video digitizer components since QuickTime 1.5.
Inside Macintosh describes the interface you must support if you wish to develop a custom interrupt function within your application. This function will be called by the video digitizer component.
Data TypesInside Macintosh defines the data structures that are used by video digitizer components, and by applications that work with video digitizers directly.
Inside Macintosh defines the flags used to denote a video digitizer's capabilities and current status. QuickTime 4 Reference adds a constant that signifies the video signal is from a television tuner.