Inside Macintosh: QuickTime Components

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VDSetPlayThruOnOff

The VDSetPlayThruOnOff function allows applications to control continuous digitization.

pascal VideoDigitizerError VDSetPlayThruOnOff
                                          (VideoDigitizerComponent ci,
                                          short state);


ci

Specifies the video digitizer component for the request. Applications obtain this reference from the Component Manager's OpenComponent function.

state

A short integer that specifies whether to use continuous digitization. The following values are valid:

digitizerOff

Turns off continuous digitization

digitizerOn

Turns on continuous digitization

When an application stops continuous digitization, the video digitizer component must restore its alpha channel, blending mask, or key color settings to graphics mode.

VDGrabOneFrame

The VDGrabOneFrame function instructs the video digitizer component to digitize a single frame of source video.

All video digitizer components must support this function.

pascal VideoDigitizerError VDGrabOneFrame
                                         (VideoDigitizerComponent ci);


ci

Specifies the video digitizer component for the request. Applications obtain this reference from the Component Manager's OpenComponent function.

VDSetupBuffers

The VDSetupBuffers function allows applications to define output buffers for use with asynchronous grabs. Video digitizer components extract information about the spatial characteristics of the video destinations from these buffers.

pascal VideoDigitizerError VDSetupBuffers
                                         (VideoDigitizerComponent ci,
                                          VdigBufferRecListHandle bufferList);


ci

Specifies the video digitizer component for the request. Applications obtain this reference from the Component Manager's OpenComponent function.

bufferList

Contains a handle to a list of output buffers. This buffer list is contained in a buffer list structure. This structure is described in "The Buffer List Structure" . Note that the video digitizer component makes a copy of the buffer list--you may dispose of this handle when the function returns to your application.

If you are developing a video digitizer component, note that the matrix field in the buffer list structure contains a pointer to the matrix structure. It is your responsibility to copy that matrix structure.

VDReleaseAsyncBuffers

The VDReleaseAsyncBuffers function allows an application to release the buffers that it allocates with the VDSetupBuffers function.

pascal VideoDigitizerError VDReleaseAsyncBuffers
                                         (VideoDigitizerComponent ci);


ci

Specifies the video digitizer component for the request. Applications obtain this reference from the Component Manager's OpenComponent function.

VDGrabOneFrameAsync

The VDGrabOneFrameAsync function instructs the video digitizer component to start to digitize asynchronously a single frame of source video. Because the component digitizes the video asynchronously, the application is free to do other things while the digitization is performed.

pascal VideoDigitizerError VDGrabOneFrameAsync
                                          (VideoDigitizerComponent ci,
                                         short buffer);


ci

Specifies the video digitizer component for the request. Applications obtain this reference from the Component Manager's OpenComponent function.

buffer

Identifies the next output buffer. The value of this parameter must correspond to a valid index into the list of buffers that you supply when your application calls the VDSetupBuffers function (which is described on VDSetupBuffers ). Note that this value is zero-based (that is, you must set this parameter to 0 to refer to the first buffer in the buffer list).

The video digitizer component uses this buffer for the next video frame (that is, the frame that will be digitized the next time the application calls the VDGrabOneFrameAsync function). In this manner, video digitizer components can quickly and efficiently prepare for the next video frame.

Some digitizer components may not allow your application to queue more than one asynchronous frame grab at a time. These components may not return control to your application until a previously requested grab has been completed.

VDDone

You can use the VDDone function in your application to determine if the VDGrabOneFrameAsync function is finished with a specific output buffer ( VDGrabOneFrameAsync is described in the previous section). Applications that use the VDGrabOneFrameAsync function to digitize video frames should call VDDone before working with a digitized image.

pascal VideoDigitizerError VDDone
                                         (VideoDigitizerComponent ci, short buffer);


ci

Specifies the video digitizer component for the request. Applications obtain this reference from the Component Manager's OpenComponent function.

buffer

Identifies the buffer for the operation. The value of this parameter must correspond to a valid index into the list of buffers you supply when your application calls the VDSetupBuffers function (which is described on VDSetupBuffers ). Note that this value is zero-based (that is, you must set this parameter to 0 to refer to the first buffer in the buffer list).

VDSetFrameRate

The VDSetFrameRate function allows an application to indicate its desired frame rate to the video digitizer. Note that some digitizers may not be able to support high frame rates.

pascal VideoDigitizerError VDSetFrameRate
                                          (VideoDigitizerComponent ci,
                                          Fixed framesPerSecond);


ci

Identifies the application's connection to the video digitizer component. An application obtains this value from the Component Manager's OpenComponent function.

framesPerSecond

Specifies the application's desired frame rate. Applications may set this parameter to 0 to return the digitizer to its default frame rate (typically 29.97 frames per second).

VDGetDataRate

The VDGetDataRate function allows an application to retrieve information that describes the performance capabilities of a video digitizer.

pascal VideoDigitizerError VDGetDataRate
                                         (VideoDigitizerComponent ci,
                                          long *milliSecPerFrame,
                                          Fixed *framesPerSecond,
                                          long *bytesPerSecond);


ci

Identifies the application's connection to the video digitizer component. An application obtains this value from the Component Manager's OpenComponent function.

milliSecPerFrame

Contains a pointer to a long integer. The video digitizer returns a value that indicates the number of milliseconds of synchronous overhead involved in digitizing a single frame. This value includes the average delay incurred between the time when the digitizer requests a frame from its associated device, and the time at which the device delivers the frame.

framesPerSecond

Contains a pointer to a fixed value. The video digitizer supplies the maximum rate at which it can capture video. Note that this value may differ from the rate that the application set with the VDSetFrameRate function, described in the previous section.

bytesPerSecond

Contains a pointer to a long integer. Video digitizers that can return compressed image data return a value that indicates the approximate number of bytes per second that the digitizer is generating compressed data, given the current compression settings and frame rate settings.