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Designing Hardware and Drivers for the Microsoft® Windows® Family of Operating Systems - page 10 / 13

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Digital Video Camcorder Support in Windows 10

The application is responsible for releasing the event when it is no longer needed, as shown in the following code fragment:

// Release event to detect device removal

hr = m_pDVcrExtTransport->GetStatus(ED_DEV_REMOVED_HEVENT_RELEASE, (long *) &hEventDevRemoved);

Managing Time-Consuming Operations

Because a DV camcorder is a physical device, a developer must consider the time lag involved in certain operations, such as ATN search. An application that controls a DV camcorder should handle time-consuming operations gracefully—notifying the user when the device is busy, maintaining a responsive user interface, and allowing the user to cancel pending operations.

The AV/C specification requires that a device must respond to a command within 100 milliseconds. However, if the requested operation cannot be completed within that time, the device can respond with a “pending” status. Unless the requesting application implements a mechanism to handle pending operations, that thread will hang until the device finishes the operation.

To handle time-consuming operations gracefully, an application should implement a secondary thread to issue the operation. This allows an application to maintain a more responsive UI because its primary thread can continue to work.

For example, an application might monitor subsequent user requests and override a pending operation if it would make sense to do so, as when the device is searching for an ATN and the user issues a stop command. Monitoring user requests also allows the application to protect the device from “button bashing”—being overwhelmed by the user issuing too many requests too quickly.

For information about using threads in applications, search topic titles for “Processes and Threads” in the Platform SDK.

Controlling MSDV from GraphEdt.exe Using the MSDV Property Page

Using Graphedt.exe (from DirectX Media SDK) you can build a number of graphs to experiment with MSDV.  Here are some of the basic graphs you can construct for capturing DV files, playback of DV files, and transmission of DV files from the computer to a DV camcorder or digital VCR (DVCR).

Capture DV to PC

This graph captures a DV stream from the camcorder to an AVI file while viewing the stream.

Playback on PC

This graph plays a DV stream from a file to an active movie window.

September 28, 2001

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