How can I extract images (JPEG or PNG or ...) from an H.264 video stream, preferably in C #?
ffmpeg can do this.
You need C # binding for ffmpeg
You can use Windows Media Foundadion.NET (link: http://sourceforge.net/projects/mfnet/ ) to decode H.264. once you do this, you can make screencap in standard ways.
FFMPEG Wrapper # . FFMPEG , .