video comes out blochy

can someone help me!
i dl a video(backup copy) of shgy dog.
i viewed the sample clip it and was fine but when i extracted tha actuall copy the video came out blotchy.
i tried extracting it again but it was the same. can someone please help me?

 

Was the preview size the same as the movie's actual size?

 

in the rar file its 738mb but when extracted it 721mb.
and i noticed that now all the films that i download are the same.
all the videos i had before came out fine it only once i saw the first blotchy and then all the ones i downloaded came like that.
please help

 

Err... samples are always encoded in higher quality.

 

its now with all the videos i download now!
help please! :-(