Question: I want to create a software:
 - Input as a video stream H264 ( from another software)
 - Output as a webcam for my friends can watch in skype, yahoo, or something like that.
 I knows I need to create directshow filter to do that, but I dont know what type filter I must to create.
 And when I have a filter, I dont know how to import it to my application?
 I need a example or a tutorial, please help me

Answer: 
You need to create a virtual video source/camera filter. There have been a dozen of questions like this on SO, so I will just link to some of them:

* [How to write an own capture filter?](https://stackoverflow.com/questions/10086897/how-to-write-an-own-capture-filter/10087276#10087276)
* [Set byte stream as live source in Expression Encoder 4](https://stackoverflow.com/questions/8488073/set-byte-stream-as-live-source-in-expression-encoder-4)
* ["Fake" DirectShow video capture device](https://stackoverflow.com/questions/1376734/fake-directshow-video-capture-device)

Windows SDK has `PushSource` sample which shows how to generate video off a filter. `VCam` sample [you can find online](http://tmhare.mvps.org/downloads.htm) shows what it takes to make a virtual device from video source.

See also: [How to implement a "source filter" for splitting camera video based on Vivek's vcam?](http://social.msdn.microsoft.com/Forums/windowsdesktop/en-US/ce717600-750b-46c0-8a63-31d65659740b/how-to-implement-a-source-filter-for-splitting-camera-video-based-on-viveks-vcam).

NOTE: Latest versions of Skype [are picky as for video devices and ignore virtual devices for no apparent reason](http://webcache.googleusercontent.com/search?q=cache:mjhhnU-9uEUJ:https://jira.skype.com/browse/SCW-3881%3FfocusedCommentId%3D58828%26page%3Dcom.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel+&cd=1&hl=en&ct=clnk&client=firefox-beta).
You should start here : [Writing DirectShow Filters](http://msdn.microsoft.com/en-us/library/windows/desktop/dd391013%28v=vs.85%29.aspx) or here : [Introduction to DirectShow Filter Development](http://msdn.microsoft.com/en-us/library/windows/desktop/dd390354%28v=vs.85%29.aspx)

I assume you already have Windows SDK for such develpment, if not check [this](http://msdn.microsoft.com/en-us/library/windows/desktop/dd375454%28v=vs.85%29.aspx)