How to Fix Video Playing Upside Down

“When I play AVI movies in Windows Media Player they are upside down. They play fine in Real, but play with the video upside down in Media Player. How can I fix this upside down problem?”
Video playing upside down is almost always a codec problem. Windows Media Player attempts to find the best codec on your system for playing back a particular type of video, but sometimes it either uses the wrong one or uses a codec with unpredictable results (like playing your video inverted). Fixing this will also fix video playing black and white and is related to needing to fix video with no audio playback problems. Almost every case of video playing upside down is related to video requiring the DivX or XviD codec. Sometimes you may have a correct version installed and it gets overwritten by installing another app. Both DivX and XviD codecs are free, although will encourage you to buy the DivX Pro upgrade, which includes some video converting tools and a few additional features. Download the free DivX codec, which also includes an automatic update check, which helps prevent this problem in the future.
To verify that DivX or XviD are actually the cause, you can use an app called MediaInfo to determine which codec you need.