Best software tool to process image/video and obtain greatest level of zoom?
You need to scale and/or crop with the best video solution. None of them do it live.


Top market solution:



  
  any Autodesk Video Solution (Smoke,Flint,Flame,Fire,Inferno). The number of options for the resample alghoritm is amazing... More than eight(8)!
  



Top open-source solution:



  
  Blender, used as a video-editor.
  


I'm sure you can easily find live solutions too, but not with the same level of quality, without going to a hardware-based solution like Blackmagic.