Downloading a video file and playing that(flv format.)

An issue??
Am providing a user to upload and download the video files.
I am using attachment_fu plugin and and usong its current_data function to get the file, and send_data to download it.
Once the downloading is complete, i was not able to play that file…

Then i saw, that the size of the file which i was playing and the same file which i am downloading is much more.
Any pointers, where i am making mistake?? or what i need to do here so that a user can play the doanloaded file…


Thanks a lot…