Yeah. Basic answer is that Cubase is not a video editing/adjusting software. What you can do - with some effort - is to buy QuicktimePro, adjust your video to length there, import this into Cubase and mix your audio. Then, with your audio edited, export the file via the youtube software.
Ha, or you could skip the whole process and edit your clips in Win7 media editor and post to youtube. My point is, Cubase is not for video work.
Cubase 6.5 (6.5.5) and 5.5 (5.5.3), WaveLab Elements 8, iC Pro remote app, LoopMash HD, Win7 64-bit, Intel C2Q9550@2.83GHz, 8G ram, Radeon HD 6570, Gigabyte X48-DS5 MB, Mackie 1640i (FireWire), M-Audio Keystation 61es controller via an M-Audio Midi-Sport 1X1.