If you follow a player on spectate you can record him but you will see the callsign and you have only a limited rotation that also depends from where the player is going
if you spectate free you can just move where you want, and its more "cinematic"
Or you can just go in a hardcore match and hold a equipment i think:
[ame=
https://www.youtube.com/watch?v=KKYpQh1BsR0]YouTube - Hardcore Parkour (Modern Warfare 2 Machinima)[/ame]