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DirectX.Capture Class Library

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29 Mar 2008Public Domain5 min read 3.9M   72K   598   1.5K
A .NET class library for capturing video and audio to AVI files.
Sample Image - DirectXCapture.jpg

Introduction

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:

C#
// 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
capture.Start();

// Stop capturing
capture.Stop();

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.

C#
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";

capture.Start();
...
capture.Stop();

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:

C#
// 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.

C#
// 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.

Credits

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

Troubleshooting

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.

License

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


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Comments and Discussions

 
Questionx64 solution Pin
Kangerm00se18-Oct-12 5:47
Kangerm00se18-Oct-12 5:47 
AnswerRe: x64 solution Pin
Michael Röttges21-Mar-13 21:45
professionalMichael Röttges21-Mar-13 21:45 
QuestionСпасибо Pin
farexg14-Oct-12 16:48
farexg14-Oct-12 16:48 
QuestionSmall avi buffer to send over the network Pin
Mihaescu Florin3-Oct-12 22:22
Mihaescu Florin3-Oct-12 22:22 
GeneralMy vote of 5 Pin
khosrow parizi19-Sep-12 6:43
khosrow parizi19-Sep-12 6:43 
QuestionDraw rectangle Pin
manganat17-Jun-12 23:02
manganat17-Jun-12 23:02 
QuestionRun time error Pin
Tiwari A K15-May-12 21:17
Tiwari A K15-May-12 21:17 
QuestionI have issue during capturing the video Pin
Member 85000363-May-12 3:49
Member 85000363-May-12 3:49 
Hello, I developed an application using your class but I have a problem during capturing video. The problem is when I try to capture video as 720p the video became faster than recored audio.

I tried to use codecs that inclued or coming as default with windows, but problem was the same. After that I chose 320x240 px resulation than it became normal. Audio and video hadnt sync issue. But I need to record min. in 800x600px resulation Frown | :( Configration of The pc which I tried to record video is, i5 cpu 8gb ram, gtx490 graphics. I think it is enough for encoding real time 720p video. (im not sure)

I wanted to use another codecs but I have no idea about encoders by the way I couldn^t find any codec Smile | :) I couldnt see the codecs that I found on your demo application.

Can you help me, thanks in advance!
Questionproblem directx.capture Pin
italiainminiatura28-Mar-12 3:48
italiainminiatura28-Mar-12 3:48 
GeneralMy vote of 5 Pin
Manoj Kumar Choubey12-Feb-12 20:39
professionalManoj Kumar Choubey12-Feb-12 20:39 
QuestionSystem.Runtime.InteropServices.COMException Pin
6739652221-Dec-11 15:39
6739652221-Dec-11 15:39 
QuestionFM tuner Pin
dino.giuditta6-Oct-11 3:17
dino.giuditta6-Oct-11 3:17 
GeneralMy vote of 5 Pin
Thiago Tozim7-Jul-11 3:30
Thiago Tozim7-Jul-11 3:30 
QuestionDirectX.Capture.dll & DShowNET.dll dlls. Pin
no_-_namee6-Jul-11 3:08
no_-_namee6-Jul-11 3:08 
AnswerRe: DirectX.Capture.dll & DShowNET.dll dlls. Pin
butterfly081525-Jul-11 19:53
butterfly081525-Jul-11 19:53 
GeneralRe: DirectX.Capture.dll & DShowNET.dll dlls. Pin
Samuel Garratt2-Oct-11 15:17
Samuel Garratt2-Oct-11 15:17 
GeneralStream Video Content Pin
psergiu30-Apr-11 6:08
psergiu30-Apr-11 6:08 
Generalpara extraer una imagen del video Pin
pakotzintote28-Apr-11 5:58
pakotzintote28-Apr-11 5:58 
GeneralRe: para extraer una imagen del video Pin
BrunoMAlves9-Nov-12 1:16
BrunoMAlves9-Nov-12 1:16 
GeneralMy vote of 5 Pin
pakotzintote28-Apr-11 5:56
pakotzintote28-Apr-11 5:56 
GeneralCapturing from 2 Webcams Pin
geko10021-Apr-11 3:39
geko10021-Apr-11 3:39 
Questionno devices of the category error on my win7 but other's computers are working. Pin
zll9999-Mar-11 14:31
zll9999-Mar-11 14:31 
AnswerRe: no devices of the category error on my win7 but other's computers are working. Pin
zll9999-Mar-11 14:39
zll9999-Mar-11 14:39 
GeneralI get this error message Pin
leonkennedy24-Feb-11 8:58
leonkennedy24-Feb-11 8:58 
GeneralAdd Watermark Pin
ifithegr85-Feb-11 1:14
ifithegr85-Feb-11 1:14 

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