This is truly one unique film. It was found on an old VHS tape. The creator either didn't discover the strange action in the background or didn't want to tell anyone about it.
But someone found the tape and published it on Archive.org (the junkyard of online videos)
See the original clip here, http://www.archive.org/details/Tape_cSummer1992Waldviertel
It was recognized and republished on Youtube, see below
This clip has been the subject to a lot of discussion on forums all over the net.
The explanation varies from a bird or an airplane. It's clearly neither.
A plane flying at this speed and altitude are bound to crash.
No known birds have this shape so it's something else.