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If you have a file with the extension .dat, it could be one of many different file types. If you believe it to be a video file, then you are probably right considering that .dat files are stored in the MPEGAV folder on VCDs. It is also sometimes used in the MPEG2 folder on SVCDs. It is basically MPEG-1 or MPEG-2 video with different headers for whiever format it is. If it is an MPEG-1 file from a VCD, then you should be able to play it with most video software such as Windows Media Player or WinDVD.
For SVCD MPEG-2 files however, an MPEG-2 codec is required unless the player you use has support for the format.
IMPORTANT</B>: These instructions are a few years old. However, we have a newer, more detailed and eloquent set of instructions for MPG / MPEG files in our Guides section. Click here to read our proper [b]How to play MPG and MPEG files article.
A great player for playing back .dat files is Media Player Classic.
Download Media Player Classic from: http://www.afterdawn.com/software/video_software/video_players/media_player_classic.cfm
Download WinDVD from: http://www.afterdawn.com/software/video_software/video_players/windvd.cfm