Unzip the zip file with the file avformat.dll (using Windows or WinZIP / WinRAR unpacker program standard).
Remove avformat.dll file from a folder and save it in the program folder, which requires avformat.dll library. 90% of users that helps.
If that does not work, you will have to extract avformat.dll in the system folder. By default, this is:
C: \ Windows \ System (Windows 95/98 / Me)
C: \ Windows \ System32 (Windows XP, Vista, 7, Win 8)
If you use a 64-bit version of Windows, you should also place the file in
C: \ Windows \ SysWOW64 \
(If the system is not on the C: drive, then look for these folders on your system drive).
How to download free avformat.dll?
Ensure that the existing files will be replaced (but make a backup of the original file for safety).
Restart the computer.