File extension BAK is given to files used for backup of another document, often created automatically by various programs or the operating system; for example, Windows may create BAK files for the System.ini and Win.ini files.

BUP (Back UP) is the filename extension of some files stored on video DVDs. The BUP file is a backup of the IFO file on a DVD, which contains the information about the organization of tracks, menus, chapters, subtitles on the disc. The BUP files are used in the event that the corresponding IFO file is unreadable, perhaps due to a scratch on the surface of the disc.

Direct Access Archive, or DAA, is a proprietary file format developed by PowerISO Computing for disk image files which supports features such as compression, password protection, and splitting to multiple volumes. It can be handled like a file just like other formats, such as an ISO image and BIN, but is currently only usable by PowerISO software. Popular disk image mounting programs such as Alcohol 120% and Daemon Tools currently do not support the mounting of DAA images.

Generic database file extension; could be created by a number of different database programs; may also be imported into multiple database programs.

The existence of two different file extensions for naming audio-only MP4 files has been a source of confusion among users and multimedia playback software. Since MPEG-4 Part 14 is a container format, MPEG-4 files may contain any number of audio, video, and even subtitle streams, making it impossible to determine the type of streams in an MPEG-4 file based on its filename extension alone. In response, Apple Inc. started using and popularizing the .m4a file extension. Software capable of audio/video playback should recognize files with either .m4a or .mp4 file extensions, as would be expected, as there are no file format differences between the two. Most software capable of creating MPEG-4 audio will allow the user to choose the filename extension of the created MPEG-4 files.

.mdf is a file suffix that designates several different file formats:

The QuickTime (.mov) file format functions as a multimedia container file that contains one or more tracks, each of which stores a particular type of data: audio, video, effects, or text (for subtitles, for example). Each track either contains a digitally-encoded media stream (using a specific codec) or a data reference to the media stream located in another file. Tracks are maintained in a hierarchal data structure consisting of objects called atoms. An atom can be a parent to other atoms or it can contain media or edit data, but it cannot do both.

MPEG-4 Part 14, formally ISO/IEC 14496-14:2003, is a multimedia container format standard specified as a part of MPEG-4. It is most commonly used to store digital audio and digital video streams, especially those defined by MPEG, but can also be used to store other data such as subtitles and still images. Like most modern container formats, MPEG-4 Part 14 allows streaming over the Internet. The official filename extension for MPEG-4 Part 14 files is .mp4, thus the container format is often referred to simply as MP4.