video files corrupted on downloading?

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This has happened to me in a back 2 back situation now, so any help is appreciated. I currently downloaded a video file of roughly 244 MB through a internet download accelerator.

It showed that the file is downloaded but when playing it with VLC media(or any other media) it played for twenty minutes than suddenly haste to the end of the timeline skipping everything in between.

For the record it is not a cracked version that i have installed. The only thing that i did was that i just installed avast internet security free version. But it has been prior three months and the problem is just emerging now.

Any help and suggestion would be appreciated.
P.S. it did not have any codec issues.