VirtualDub: (Free - open source).
Software:
VirtualDub download (at SourceForge) - virtualdub.org
Documentation and program forums:
Welcome to virtualdub.org! - virtualdub.org
1) Download and install VirtualDub from the website indicated above.
2) Run the program and open your video into the program.
3) Go to Video under the menu and click Full Processing Mode.
4) Press Ctrl-F (or go to Video->Filters) to open the Filters Dialogue box.
5) Click Add and choose Rotate from the filters shown. You will have
the option then to choose how you wish to rotate the video.
6) Click OK to get back to the main VirtualDub program window. You
may now do any further editing you require to the video using the
program.
7) To rotate the video you should now save the video as a new file and
the process will begin. Please note that this may take some time
depending on the speed of your PC and what further options you have
chosen.
You may need to download and install an MP4 codec, if you don't already have one.
Ken