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Posted 26 Jan 2003


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DirectX.Capture Class Library

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4.94/5 (227 votes)
29 Mar 2008Public Domain5 min read
A .NET class library for capturing video and audio to AVI files.
Sample Image - DirectXCapture.jpg


This article presents a class library for capturing audio and video to AVI files in .NET. Some of the features of this library:

  • List and select hardware devices
  • Access to common audio and video settings (e.g. frame rate, size)
  • Support audio and video compression codecs
  • Support video preview
  • Support TV tuners
  • Support crossbars and audio mixers
  • Retrieve device capabilities
  • Show property pages exposed by drivers
  • MSDN-style documentation included

Using the Code

The Capture class is the core of this library. Here is a simple example:

// Remember to add a reference to DirectX.Capture.dll
using DirectX.Capture

// Capture using the first video
// and audio devices available
Capture capture = new Capture( Filters.VideoInputDevices[0],
                               Filters.AudioInputDevices[0] );

// Start capturing

// Stop capturing

Remember to add a reference in your project to DirectX.Capture.dll. This DLL requires DShowNET.dll, so make sure they are both in the same directory. Once you add the reference, Visual Studio .NET should take care of the copying for you.

This example will capture video and audio using the first video and audio devices installed on the system. To capture video only, pass a null as the second parameter to the constructor.

The class is initialized to a valid temporary file in the Windows temp folder. To capture to a different file, set the Capture.Filename property before you begin capturing.

A Second Example

This next example shows how to change video and audio settings. Properties such as Capture.FrameRate and Capture.AudioSampleSize allow you to programmatically adjust the capture. Use Capture.VideoCaps and Capture.AudioCaps to determine valid values for these properties.

Capture capture = new Capture( Filters.VideoInputDevices[0],
                               Filters.AudioInputDevices[1] );

capture.VideoCompressor = Filters.VideoCompressors[0];
capture.AudioCompressor = Filters.AudioCompressors[0];

capture.FrameRate = 29.997;                 // NTSC
capture.FrameSize = new Size( 640, 480 );   // 640x480
capture.AudioSamplingRate = 44100;          // 44.1 kHz
capture.AudioSampleSize = 16;               // 16-bit
capture.AudioChannels = 1;                  // Mono

capture.Filename = "C:\MyVideo.avi";


The example above also shows the use of video and audio compressors. In most cases, you will want to use compressors. Uncompressed video can easily consume over 1GB of disk space per minute. Whenever possible, set the Capture.VideoCompressor and Capture.AudioCompressor properties as early as possible. Changing them requires the internal filter graph to be rebuilt which often causes most of the other properties to be reset to default values.

Behind the Scenes

This project uses 100% DirectShow to capture video. Once a capture is started, DirectShow spawns another thread and handles retrieving/moving all the video and audio data itself. That means you should be able to capture at the same speed and quality as an application written in C.

DirectShow is implemented as a set of COM components and we use .NET Interop to access them. The pioneering work on this was done by NETMaster with the DShowNET project. This Capture library uses DShowNET for the interop layer with only a few extensions. This is the DShowNET.dll mentioned earlier.

Sitting on top of all of this is the Capture class library. The center of any DirectShow app is the filter graph and the filter graph manager. For a good overview, see The Filter Graph and Its Components from the MSDN.

The Least Work Possible

The library tries at all times to do the least amount of work possible. The problem is: DirectShow is very flexible, but has few firm standards for driver developers and I have limited hardware to test with. As a result, the class tries to avoid doing any work that may not be necessary, hopefully avoiding potential incompatibilities in the process.

One example is video preview. You can start and stop preview with:

// Start preview
capture.PreviewWindow = myPanelControl;

// Stop preview
capture.PreviewWindow = null;

Hopefully this is simple to use. Internally, DirectShow does a lot of work: add required upstream filters for WDM devices, search for preview pins, use the Overlay Manager for video ports (hardware overlays), insert SmartTee filters when a separate preview pin is not available and more. Instead of rendering the preview stream as soon as the class is created, the class waits until the PreviewWindow property is set.

For developers who don't need preview, none of this work will ever be done. That means your application is more likely to work on a wider range of hardware. For developers that do need preview, this makes it easier to locate the cause of the problem and fix it or handle it gracefully.

Performance Tips

Many of the properties on the Capture class are retrieved directly from the underlying DirectShow COM components. If you need to refer to the property repeatedly in a block of code, take a copy of the value and use your copy.

// AudioSampleSize is retrieved from DirectShow each iteration
for ( int c = 0; c < 32; c++ )
    if ( c == capture.AudioSampleSize )
        MessageBox.Show( "Found!" );

// A faster solution
int x = capture.AudioSampleSize;
for ( int c = 0; c < 32; c++ )
    if ( c == x )
        MessageBox.Show( "Found!" );

Why doesn't the class simply cache the value internally? We don't know when the filter (device driver) will change this value, so we have to retrieve the value every time. This means you will always get the real value of the property.


The DirectShow interop layer was developed by NETMaster in the DShowNET project. The MDSN-style documentation was generated from the source code using nDoc.


I have tested this with an Asus v7700 (NVidia GeForce2, reference drivers) and my onboard sound card. I can't guarantee any other hardware will work. However, I expect most video capture cards and sound cards will work. You may have trouble with TV Tuner cards and DV devices (Firewire camcorders) though they should be solvable.

Try the AMCap sample from the DirectX SDK (DX9\Samples\C++\DirectShow\Bin\AMCap.exe) or Virtual VCR, a free DirectShow capture application.

This class library uses COM Interop to access the full capabilities of DirectShow, so if there is another application that can successfully use a hardware device then it should be possible to modify this class library to use the device. Please post your experiences, good or bad, in the forum below.

User Enhancements

The following enhancements have been posted to the discussion board:

Thanks to fdaupias and dauboro for their submissions. I have not had time to post a tested, updated version with these enhancements. If anyone wants to make an updated download zip, mail it to me and I will added it to this page. Keep the enhancements coming.

DirectX.Capture Wiki

A Wiki for this project is available here. This Wiki can be edited by anyone, no registration is required. I hope this Wiki will allow interested users to more easily collaborate on this project. New versions, enhancements, tips and tricks can be posted on the Wiki.


This article, along with any associated source code and files, is licensed under A Public Domain dedication

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Comments and Discussions

QuestionNo devices of the category Pin
Tengeneng Yan9-Sep-20 21:50
MemberTengeneng Yan9-Sep-20 21:50 
QuestionPlease help Pin
Member 1292966129-Sep-19 23:59
MemberMember 1292966129-Sep-19 23:59 
QuestionCapture is not updating and I can click on picturebox Pin
Member 1383010718-May-18 6:31
MemberMember 1383010718-May-18 6:31 
QuestionVideo Size Minimize Pin
Member 115357061-Jul-16 3:49
MemberMember 115357061-Jul-16 3:49 
QuestionError : "A required privilege is not held by the client. (Exception from HRESULT: 0x80070522" Pin
Member 1065263116-Jun-16 0:54
MemberMember 1065263116-Jun-16 0:54 
AnswerRe: Error : "A required privilege is not held by the client. (Exception from HRESULT: 0x80070522" Pin
Ahmed Hamdy4-Sep-16 17:38
MemberAhmed Hamdy4-Sep-16 17:38 
QuestionProblem of CaptureTest in Visual Studio Pin
Member 123993791-Apr-16 4:15
MemberMember 123993791-Apr-16 4:15 
QuestionWorks by this method also capture desktop? Pin
Member 141858012-Jan-16 3:34
MemberMember 141858012-Jan-16 3:34 
QuestionNot save as AVI file, send to another component Pin
jack_j2316-Oct-15 0:48
Memberjack_j2316-Oct-15 0:48 
QuestionThe demo project doesnot work wit startech video capture card Pin
Gourav Sharma from Jammu27-Mar-15 22:22
MemberGourav Sharma from Jammu27-Mar-15 22:22 
GeneralMy vote of 5 Pin
Metafunken2-Mar-15 2:19
MemberMetafunken2-Mar-15 2:19 
SuggestionThere is an update available for your article Pin
Elmue11-Oct-14 6:13
MemberElmue11-Oct-14 6:13 
Questionhow can i change bitrate of output video file! Pin
son0nline22-Sep-14 16:33
Memberson0nline22-Sep-14 16:33 
QuestionPreview size Pin
Marnold610226-Aug-14 10:41
MemberMarnold610226-Aug-14 10:41 
AnswerRe: Preview size Pin
Member 110593634-Sep-14 7:36
MemberMember 110593634-Sep-14 7:36 
Questionhow to only display video and not save any file? Pin
Member 1101579815-Aug-14 17:50
MemberMember 1101579815-Aug-14 17:50 
AnswerRe: how to only display video and not save any file? Pin
Member 110593634-Sep-14 7:49
MemberMember 110593634-Sep-14 7:49 
QuestionHow do I rotate a camera view got with DirectX in Vb.Net ? Pin
Olayèmi Ouabi12-May-14 23:08
MemberOlayèmi Ouabi12-May-14 23:08 
QuestionDIsplay YUV Pin
tieugiang9415-Apr-14 0:31
Membertieugiang9415-Apr-14 0:31 
Questioncapture desktop as image Pin
Member 107369579-Apr-14 16:47
MemberMember 107369579-Apr-14 16:47 
Questionhow i save image to folder in c# Pin
Soahib jamil2-Apr-14 19:10
MemberSoahib jamil2-Apr-14 19:10 
QuestionIt's not work right Pin
tieugiang9414-Mar-14 21:02
Membertieugiang9414-Mar-14 21:02 
QuestionGetting error Pin
Member 87728507-Feb-14 7:50
MemberMember 87728507-Feb-14 7:50 
QuestionUSB Composite Adapter + Crossbar Pin
cw229030-Nov-13 7:20
Membercw229030-Nov-13 7:20 
AnswerRe: USB Composite Adapter + Crossbar Pin
free5lot29-Dec-13 22:08
Memberfree5lot29-Dec-13 22:08 

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