A pop-up notice saying a video file is damaged is the digital equivalent of the "check engine" light on your car. It doesn't tell you what the problem is or how to fix it. The notice just serves as a frustratingly vague notification that something is going on. Just like engine problems, video files can be damaged in any number of ways and fixing them is never a sure thing. While several programs dedicating to repairing video exist, when they do work they lead to other problems, particularly non-synced audio and video. A safer bet is to try to repair the file through a basic video player like those listed below.
Download and install the free VLC media player from the link in "Resources." VLC is known for being the most compatible video player and still your best shot at repairing that file.
Open your video file with VLC. There's a chance it will just start playing; VLC can sometimes play video files other applications claim are damaged. If it doesn't, you will see a pop-up window informing you the file is damaged.
Click the "Repair" button. This process could take several minutes or more.
Using Windows Media Player or Quicktime
Download and install Windows Media Player or Quicktime from the links under "Resources" if you do not have them already. See the "Tips" section if you are unsure which is right for your file.
Open the video with the application. You will see a pop-up window informing you of the error.
Select the option to try to repair the file or, if available, download the codec to play it. If the window simply presents you with an error message and an "OK" button, your video cannot be repaired with this program.
If your video is in MPEG or WMV format, Windows Media Player is your best bet. If it is a MOV or AVI file, try Quicktime. If you don’t know or your video is in another format, try Quicktime first. Since Quicktime can play more file types than Windows Media Player, it presents a higher probability of success.
Many damaged video files simply cannot be repaired. For instance, if the file was incompletely downloaded from the internet (a common reason for the "damaged" message), no program can magically restore the missing data.