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---
page_type: sample
description: "An AVStream filter-centric simulated capture sample driver with functional audio."
languages:
- cpp
products:
- windows
---
<!---
name: AVStream filter-centric simulated capture sample driver (Avssamp)
platform: WDM
language: cpp
category: Camera
description: An AVStream filter-centric simulated capture sample driver with functional audio.
samplefwlink: http://go.microsoft.com/fwlink/p/?LinkId=620186
--->
# AVStream filter-centric simulated capture sample driver (Avssamp)
The AVStream filter-centric simulated capture sample driver (Avssamp) provides a filter-centric [AVStream](http://msdn.microsoft.com/en-us/library/windows/hardware/ff554240) capture driver with functional audio. This streaming media driver performs video captures at 320 x 240 pixel resolution in RGB24 or YUV422 format while playing a user-provided Pulse Code Modulation (PCM) wave audio file in a loop. The sample demonstrates how to write a filter-centric AVStream minidriver.
Installation instructions
-------------------------
1. Copy AVssamp.inf to a directory, for example, C:\\Avstream\\.
2. In this directory, create a new subdirectory named objfre\_x86 if the target operating system is x86-based, or objfre\_amd64 for an x64-based target operating system, for example, C:\\AVstream\\objfre\_x86\\.
3. Copy the processor-appropriate Avssamp.sys file to the objfre\_\* directory.
4. Start a command prompt with administrator privilege and run the processor-specific WDK tool Devcon.exe to launch the installation. For example:
`C:\WinDDK\7600.16384.0\tools\devcon\i386\devcon.exe install C:\AVstream\avssamp.inf SW\{20698827-7099-4c4e-861A-4879D639A35F}`
Programming Tour
----------------
[**DriverEntry**](http://msdn.microsoft.com/en-us/library/windows/hardware/ff558717) in Avssamp.cpp is the initial point of entry into the driver. This routine passes control to AVStream by calling [**KsInitializeDriver**](http://msdn.microsoft.com/en-us/library/windows/hardware/ff562683). In this call, the minidriver passes the device descriptor, an AVStream structure that recursively defines the AVStream object hierarchy for a driver. This is common behavior for an AVStream minidriver.
Filter.cpp is where the sample lays out the [**KSPIN\_DESCRIPTOR\_EX**](http://msdn.microsoft.com/en-us/library/windows/hardware/ff563534) structure for the single capture pin. Audio.cpp contains the **KSPIN\_DESCRIPTOR\_EX** structure for the audio capture pin. This pin is dynamically created only if C:\\avssamp.wav exists and is a valid and readable PCM format wave file.
The filter dispatch structure [**KSFILTER\_DISPATCH**](http://msdn.microsoft.com/en-us/library/windows/hardware/ff562554) in Filter.cpp provides dispatches to create and process data. The **DispatchProcess** method is defined inline in Filter.h. It calls the **Process** method in Filter.cpp in the context of the **CCaptureFilter** class. Be aware that the process dispatch is provided in **KSFILTER\_DISPATCH** because this sample is filter-centric.
Audio.cpp lays out a [**KSPIN\_DISPATCH**](http://msdn.microsoft.com/en-us/library/windows/hardware/ff563535) pin dispatch structure, which contains the dispatch table for the audio pin. Be aware that the **Process** member of this structure is **NULL** because the sample is filter-centric. Similarly, Video.cpp contains the **KSPIN\_DISPATCH** structure for the video capture pin, again with the **Process** member set to **NULL**.
For more information, see the comments in all .cpp files.
File Manifest
-------------
File | Description
-----|----------
Audio.cpp | Audio capture pin implementation.
Audio.h | Header file for Audio.cpp.
Avssamp.cpp | Main file for the AVStream filter-centric sample.
Avssamp.h | Main header for the AVStream filter-centric sample.
Avssamp.inf | Installation information for the AVStream sample driver (avssamp.sys).
Capture.cpp | Capture pin implementation for all capture pins on the sample filter.
Capture .h | Capture pin level header for all capture pins on the sample filter.
Filter.cpp | Capture filter implementation (including frame synthesis) for the fake capture filter.
Filter.h | Filter level header for the filter-centric capture filter.
Image.cpp | Image synthesis and overlay code. These objects provide image synthesis (pixel, color-bar, etc) onto RGB24 and UYVY buffers as well as software string overlay into these buffers.
Image.h | Image synthesis and overlay header.
Purecall.h | _purecall stub necessary for virtual function usage in drivers.
Video.cpp | Video capture pin implementation.
Video.h | Video capture pin header.
Wave.cpp | Wave object implementation
Wave.h | Wave object header
|
