A few times happened to me to record a video with my picture camera turned in portrait mode. It always looks nice on camera but, as soon as you watch it on the pc screen, you realize that something went wrong... :-|
Fortunately there is some software that can sort this problem out for us. Today I tried Avidemux and I got surprised with the easiness of the process and the quality of the result obtained.
Avidemux is a nice open-source program designed for video editing. It's platform independent so that it runs under Windows, Mac OS X, Linux and BSD. The version tried is 2.5.2 so, depending on your version/OS and GUI (GTK or QT) it might look different but the actions to take are simply the following (see screenshot):
1) make sure to select the format of the "Video" to produce (you can't leave just "copy");
2) open the pop up window refereed to "Filters";
3) select the filter "Transform";
4) select the filter "Rotate" and add it (another little window will pop up);
5) choose how you want to rotate the video, click "OK" and "Close" the Video Filter Manager Window;
6) it's time to save the file. Give it a name and let Avidemux do the job for you. Done?