Road Map to QuickTime 3

Clock Components

Clock components provide two basic services: they generate time information, and they schedule time-based callback events. The Movie Toolbox is the primary user of clock components, but applications may use clock components to schedule application-defined callback events. A clock component provides real-time clock information derived from a hardware source.

Applications developers should read the section "About Clock Components" for general information, and may want to refer to the sub-section "Using the Callback Functions." The remainder of this chapter is of interest only to programmers who are creating a clock component.

There have been no changes to the clock component API since QuickTime 1.5. All of the information in this chapter can be found in Inside Macintosh: QuickTime Components.

About Clock Components

Inside Macintosh describes the general features of clock components and provides diagrams showing the relationship between applications, the Movie Toolbox, and clock components.

Clock Component Functions

Inside Macintosh defines the functions which clock components must support, the callback functions that a clock component may optionally support, and functions which the Movie Toolbox will use to alert a clock component of changes in the environment. Applications programmers may be interested in the callback functions. The other functions are documented for developers who wish to create new clock components.

Your application can call any clock component function at interrupt time, except for the ClockNewCallBack and ClockDisposeCallBack functions. In addition, your application should not call the Component Manager's OpenComponent or CloseComponent functions at interrupt time.

• Getting the Current Time
• ClockGetTime
• Using the Callback Functions
• ClockNewCallBack
• ClockCallMeWhen
• ClockCancelCallBack
• ClockDisposeCallBack
• Managing the Time
• ClockTimeChanged
• ClockRateChanged
• ClockStartStopChanged
• ClockSetTimeBase

Movie Toolbox Clock Support Functions

Inside Macintosh defines several function provided by the Movie Toolbox to help clock components manage callback functions. These functions can all be called at interrupt time. These functions should only be called by clock components.

• AddCallBackToTimeBase
• ExecuteCallBack
• RemoveCallBackFromTimeBase
• GetFirstCallBack
• GetNextCallBack

Data Type

Inside Macintosh defines the data type QTCallBackHeader, used by clock components to communicate scheduling data about callback events to the Movie Toolbox.

Constants

Inside Macintosh defines the capability flags and component types used by clock components.

• Component Capability Flags for Clocks
• Component Types for Clocks