Among other things there was a program called Motion mentioned in the article above. I found out that a quit new version of that program was already in the current Debian Distribution. So as soon as I had a working video device I installed it. Motion is a nice piece of software for detecting motion in video streams that is developed by volunteers within the Linux community. From the projects website and mailing list I received a lot of valuable information. Example: Despite of providing the recommended version of Ffmpeg for Debian my Motion was unable to encode mpeg-movies on the fly. But this seemed to be a regular problem to include support for Ffmpeg into Motion, since I found several questions with relation to this problem on the motion mailing list and with them the solution.

Going behind the scenes
Finally I had to load the sources and compiled Ffmepg and Motion on my own. After all it was not too hard, even applying the webcam-leak-limit-patch and, most important, it worked very nice for the moment. Later I started reading the files in the source directory. Here are some results from that might be of interest at least for users of Motion. If you find it useful too, follow the links below. There are patches for upgrading the original source code v3.1.10 and others for (incremental) upgrading from the previous version of that patch. Because the patches modify only 'video.c' for now I'm quit sure they don't interfere with the webcam-leak-limit-patch from the Motion website. However, keep in mind it's a newbies work. If you find a problem, please report it to me. Thanks.

1) Capability to draw text
2) to be continued ...