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DVD File Systems

All DVD discs use the UDF (Universal Disk Format) file system, designed for both read-only and recordable discs.


A new file system was chosen for DVD which would suit both read-only and writable versions. This file system is a subset of UDF (Universal Disk Format) called micro UDF (M-UDF).  The main characteristics of UDF are:

  • Robust file exchange
  • System & vendor independent
  • Writable & read-only media
  • Based on ISO 13346

UDF has been extended to provide the necessary features for both write-once and rewritable discs.  A combination of UDF and ISO 9660 (known as UDF Bridge) is used on some DVD discs to provide compatibility with existing operating systems, including Windows95.  Applications can access the data files using either ISO 9660 or UDF file structures, but the use of UDF is recommended.  

Directory Structure

The directory structure of a DVD disc is as shown below, where only the VIDEO_TS and AUDIO_TS directories are mandatory.  Files which are not for DVD-Video or DVD-Audio are contained in other directories as required by the application.

DVD Directory Structure

  • DVD-Video discs use only UDF (not ISO 9660) with all required data specified by UDF and ISO 13346 to allow playing in computer systems.  The DVD-Video files must be no larger than 1 GB in size and be recorded as a single extent (ie in one continuous sequence).  The first directory on the disc must be the VIDEO_TS directory containing all the files.  All filenames are 8.3 format.  All other files not included in the DVD-Video specification will be ignored by DVD-Video players.
  • DVD-Audio discs also only use UDF and files are contained in the AUDIO_TS directory.
  • DVD-ROM discs use UDF (plus ISO 9660 for compatibility with Windows95). The UDF Bridge specification does not explicitly include the Joliet extensions for ISO 9660 which are needed for long filenames.


UDF Bridge
A combination of UDF and ISO 9660 file system formats that provides backward-compatibility with ISO 9660 readers while allowing full use of the UDF standard.

UDF (Universal Disc Format)
A standard developed by the Optical Storage Technology Association designed to create a practical and usable subset of the ISO/IEC 13346 recordable, random-access file system and volume structure format.

universal DVD
A DVD designed to play in DVD-Audio and DVD-Video players (by carrying a Dolby Digital audio track in the DVD-Video zone).

universal DVD player
A DVD player that can play both DVD-Video and DVD-Audio discs.

user data
The data recorded on a disc independent of formatting and error-correction overhead. Each DVD sector contains 2048 bytes of user data.