I took a video with my camera tilted 90 degrees and wanted to correct that with ffmpeg. You use the video filter (-vf) transpose. A value of 1 does 90 degrees clockwise, and a value of 2 does counter-clockwise.

ffmpeg -y -i PICT0005.AVI -r 30 -ar 16000 -vb 1000k -vf transpose=1 /tmp/out.mp4