So, you have downloaded a 4.2 GB movie and now you can't watch it because a few KB of it are corrupted?
1) Download zidrav-3.5-bin.tar.gz
and extract it with your favourite extractor, preferrable 7zip
. Zidrav is 82 KByte and does not install anything.
2) Start it, click on "make Checksum File", draw the file onto the "Input File" line, click go. It will generate a .CDT file of small size.
3) Find someone who has a non-corrupted version of the file, send him your .CDT file. Have him start zidrav and select "Make patch file". It will generate a patch. The more of your file is corrupted the bigger it will be. Have him send it to you.
4) Select "Apply patch file" and apply it to your corrupted file.
Note: you might also start by having the person who has the non-corrupted file "make checksum file" and so on, this will require 1 more step.