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What are UNDEFINED files and how to open them

Are you having problems opening an UNDEFINED file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your UNDEFINED files.

What is an UNDEFINED file?

The .undefined file extension is used for various file formats that cannot be recognized by the system. Some file recovery tools use this file extension to label recovered files that have not been completely restored. Other programs like Web browsers and email applications may label downloaded or attached files with unknown file types as UNDEFINED files.The content of these .undefined files varies, depending on the actual format of the files. For example, a data recovery application that has failed to completely restore a JPG file may label the file as an UNDEFINED file, and this .undefined file may contain corrupted image data. On the other hand, a Web browser that fails to recognize an AVI file that has been downloaded from the Internet may label the digital video file as an UNDEFINED file. This .undefined file may contain digital video, but there is no guarantee that the .undefined file will play in a standard AVI player.It's best to leave these .undefined files alone. In most instances, these UNDEFINED files contain corrupted data and are from unknown sources.

How to open UNDEFINED files

Important: Different programs may use files with the UNDEFINED file extension for different purposes, so unless you are sure which format your UNDEFINED file is, you may need to try a few different programs.

While we have not verified the apps ourselves yet, our users have suggested two different UNDEFINED openers which you will find listed below.

Last updated: June 1, 2021

Various apps that use files with this extension

These apps are known to open certain types of UNDEFINED files. Remember, different programs may use UNDEFINED files for different purposes, so you may need to try out a few of them to be able to open your specific file.

KMPlayerKMPlayerUser submitted
GOM PlayerGOM PlayerUser submitted

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File.org helps thousands of users every day, and we would love to hear from you if you have additional information about UNDEFINED file formats, example files, or compatible programs. Please use the links below or email us at submit@file.org to discuss further.