UDF:
An aspect of the overall DVD specification with major ramifications is the across-the-board adoption of the UDF (Uniform Data Format) file system based on ISO1336. This was adopted to be cross-platform capable, allow for read and writeability and sell movies among other things. This is one of the few absolutely definitive aspects of this project. There is no equivalence to a partition such as exists on hard drive with DVD (at least on a single disk layer), the whole disk is one UDF volume.
Fortunately, the DVD Forum incorporated one thing that allows us to work with the medium. In addition to the inclusion of video_ts and audio_ts folders to store respective content for the two types of media they've been selling for 50 years, they allowed for...(drumroll)...other folders!!! Gee, thanks guys. I point out here that the video_ts folder has to be first on the disk on order to be DVD-V compliant.
Just as fortunately, ISO9660 specifies a UDF bridge. The ISO 9660 data starts at track time 00:02:16 or sector 166 (logical sector 16) of track one. For a multisession disc (write-once or pressed) the ISO 9660 data will be in the first data track of each session containing data tracks. Simply put, this allows the ISO9660 folder to be seen even though it lives on UDF.
It's unclear how (or if) ISO9660 is officially incorporated into UDF. Maybe it's just a trick someone discovered. It's possible that the manufactures voluntarily adopted it. DVD-ROM discs use UDF plus ISO 9660 for compatibility with Windows95 and Mac in certain cases as we shall see. At the end of the day, it's unimportant. The presence of a UDF bridge on the disk doesn't seem to cause problems with other platforms and environments and neither does the folder it identifies.
DVD formats that attempted to make fuller use of online capability such as iDVD (not to be confused with Apple's iDVD authorware) stalled for lack of interest. Attempts to push web-enabled DVD ("convergent") devices similarly lost momentum. Not surprisingly, the hype-phase of iDVD and web-enabled players was the crest of the dot-com boom. The subsequent stall followed dot-com's crash as well. This is not to say that interesting work doesn't continue by some notable pioneers such as Interactual Media, Sonic Systems (now Interactual's parent), PlanetWeb and Sigma Systems along hardware and software lines.
This video_ts folder contains three types of files that are recognized by the set-top OS:
1. IFO (InFO) files which contain all of the indexing information and the content
presentation data like menu structures and options.
2. BUP (BackUP) files are duplicates of IFOs above. Since DVD is a relatively
corruption-resistant media and since any damage to the IFOs would likely be physical
(therefore effecting IFO and BUP file alike) and since most DVDs are write-incapable
they don't get used for much. However, if physical damage to the disk exists, BUP files
contain a mixture of redundant information and EEC or parity (not sure which) data that
allow on-the-fly error correction in content streams.
3. VOB (Video Object) files are the content itself. These are called by the player
software using IFO file content.