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DVD
File
Systems
All DVD discs use the UDF 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-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.
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