Rotating a video on Linux is as easy as follows:
- get the avidemux programme
- open it, open the original video
- save the video to a new location
- select Video – <codec you want>
- select the newly appeared Filter button
- add Rotate, configure degrees
- save the video file again – the programme will start to decode. You can select ‘shutdown when finished’. Rotating a video of 10MB took just some minutes..