---
page_type: sample
description: "An AVStream filter-centric simulated capture sample driver with functional audio."
languages:
- cpp
products:
- windows
- windows-wdk
---

# AVStream filter-centric simulated capture sample driver (Avssamp)

The AVStream filter-centric simulated capture sample driver (Avssamp) provides a filter-centric [AVStream](https://docs.microsoft.com/windows-hardware/drivers/stream/avstream-overview) 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\\.

1. 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\\.

1. Copy the processor-appropriate Avssamp.sys file to the objfre\_\* directory.

1. 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**](https://docs.microsoft.com/previous-versions//ff558717(v=vs.85)) in Avssamp.cpp is the initial point of entry into the driver. This routine passes control to AVStream by calling [**KsInitializeDriver**](https://docs.microsoft.com/windows-hardware/drivers/ddi/content/ks/nf-ks-ksinitializedriver). 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**](https://docs.microsoft.com/windows-hardware/drivers/ddi/content/ks/ns-ks-_kspin_descriptor_ex) 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**](https://docs.microsoft.com/windows-hardware/drivers/ddi/content/ks/ns-ks-_ksfilter_dispatch) 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**](https://docs.microsoft.com/windows-hardware/drivers/ddi/content/ks/ns-ks-_kspin_dispatch) 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 |